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Explain equivalence reasoning

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5401583
Diagram b) shows diagram a) after the paper is turned a quarter-turn. Write the shaded fraction in each diagram. Explain why turning the paper does not change the fraction represented.
Figure for problem 540158

Hints

- Count the equal parts and shaded parts in diagram a). - Do the same count in diagram b) instead of judging by which way the rectangle points. - Decide whether a turn changes the size of the whole or any of its parts.

Solution

1. In diagram a), the rectangle is divided into \(4\) equal parts and \(3\) are shaded, so it represents \(\frac{3}{4}\). 2. In diagram b), the same rectangle is still divided into the same \(4\) equal parts and the same \(3\) parts are shaded, so it also represents \(\frac{3}{4}\). 3. A quarter-turn changes only the direction of the paper. It does not change the whole, the equal parts, or which parts are shaded. 4. Therefore, both diagrams represent \(\frac{3}{4}\).

Answer

Both diagrams represent \(\frac{3}{4}\). Turning the paper changes its direction but not the whole, its \(4\) equal parts, or the \(3\) shaded parts.
5401133
Use the two same-size bars. Explain why their shaded fractions are equivalent, and write the equality.
Figure for problem 540113

Hints

- Count the equal parts and shaded parts in each same-size bar. - Compare where the shaded regions end. - Explain how one partition could be refined to make the parts line up with the other partition.

Solution

1. Bar a) shows \(1\) of \(3\) equal parts shaded, or \(\frac{1}{3}\). 2. Bar b) shows \(2\) of \(6\) equal parts shaded, or \(\frac{2}{6}\). 3. Splitting one third into \(2\) equal pieces makes two sixths without changing the shaded length. 4. Therefore, \(\frac{1}{3}=\frac{2}{6}\).

Answer

One third can be split into \(2\) equal sixths, so \(\frac{1}{3}=\frac{2}{6}\).
5401153
Use the two same-size bars. Explain why their shaded fractions are equivalent, and write the equality.
Figure for problem 540115

Hints

- Read the shaded fraction in each model. - Compare the shaded lengths of the same-size bars. - Explain how the larger parts in one model can be split to match the smaller parts in the other model.

Solution

1. Bar a) shows \(3\) of \(4\) equal parts shaded, or \(\frac{3}{4}\). 2. Bar b) shows \(6\) of \(8\) equal parts shaded, or \(\frac{6}{8}\). 3. Splitting every fourth into \(2\) equal pieces makes \(8\) equal parts and \(6\) shaded parts without changing the shaded amount. 4. Therefore, \(\frac{3}{4}=\frac{6}{8}\).

Answer

Splitting every fourth into \(2\) equal pieces makes \(8\) equal parts and \(6\) shaded parts. The shaded amount stays the same, so \(\frac{3}{4}=\frac{6}{8}\).
5401313
Someone claims that adding \(1\) to the numerator and denominator keeps a fraction equivalent, so \(\frac{2}{3}=\frac{3}{4}\). Use the models to explain why this rule is false.
Figure for problem 540131

Hints

- Compare the unshaded part in each same-size whole. - One model leaves one third unshaded; the other leaves one fourth unshaded. - Different unshaded amounts mean different shaded amounts.

Solution

1. Two thirds leave one third of the first whole unshaded. 2. Three fourths leave one fourth of the second same-size whole unshaded. 3. One third is larger than one fourth, so the shaded amounts are different. 4. Therefore, \(\frac{2}{3}\ne\frac{3}{4}\).

Answer

The rule is false. The models show different shaded amounts, so \(\frac{2}{3}\ne\frac{3}{4}\).
5401373
Each bar represents the same-size whole. Use the three models. Write the fraction shown by each bar. Are the three fractions equivalent? Explain how the number and size of the equal parts change while the shaded amount stays the same.
Figure for problem 540137

Hints

- Count the total parts and shaded parts in each model. - Compare the endpoint of the shaded region across the three same-size bars. - Ask what happens to the part size when the same whole is divided into more equal pieces.

Solution

1. Model a) shows \(1\) of \(2\) equal parts shaded, so it represents \(\frac{1}{2}\). 2. Model b) shows \(2\) of \(4\) equal parts shaded, so it represents \(\frac{2}{4}\). 3. Model c) shows \(3\) of \(6\) equal parts shaded, so it represents \(\frac{3}{6}\). 4. Each bar has the same shaded length. Dividing the same half into smaller equal pieces increases both the number of total parts and the number of shaded parts without changing the shaded amount. Therefore, \(\frac{1}{2}=\frac{2}{4}=\frac{3}{6}\).

Answer

The models show \(\frac{1}{2}\), \(\frac{2}{4}\), and \(\frac{3}{6}\). They are equivalent because each shades the same half of a same-size whole even though that half is partitioned into different numbers of equal pieces.
5401443
A circle has \(\frac{1}{2}\) shaded. A rectangular card has \(\frac{2}{4}\) shaded. Explain why the fractions are equivalent even though the wholes and their parts have different shapes.
Figure for problem 540144

Hints

- Count the equal parts in each whole. - Count the shaded parts in each model. - Decide whether both models show one half.

Solution

1. Each shape is divided into equal parts. 2. One of two equal parts is shaded in the circle, so it shows one half. 3. Two of four equal parts are shaded in the card, so it also shows one half. 4. The part shapes are different, but both models show the same fraction: \(\frac{1}{2}=\frac{2}{4}\).

Answer

Both models show one half of their whole, so \(\frac{1}{2}=\frac{2}{4}\). The shapes of the parts do not change the fraction.
5401523
On a number line, \(\frac{3}{4}\) is one fourth-size space to the left of \(1\). The point \(\frac{6}{8}\) is two eighth-size spaces to the left of \(1\). Explain why these descriptions place the fractions at the same point.
Figure for problem 540152

Hints

- Compare the length of two eighth-size spaces with one fourth-size space. - Both fractions are measured left from the same point, \(1\). - Equal distances from \(1\) land at the same point.

Solution

1. Two eighth-size spaces have the same total length as one fourth-size space. 2. Both points are therefore the same distance to the left of \(1\). 3. A single number line has only one point at that distance from \(1\). 4. Thus, \(\frac{3}{4}=\frac{6}{8}\).

Answer

Two eighths equal one fourth, so both fractions are one fourth below \(1\). Therefore, \(\frac{3}{4}=\frac{6}{8}\).
5401683
Use the bar model. Eli says, “The shaded fraction is equal to \(\frac{2}{3}\) because both fraction names leave two parts unshaded.” Is Eli's explanation correct? Replace it with a correct explanation.
Figure for problem 540168

Hints

- First read the shaded fraction from the model. - Ask whether “two parts” means pieces of the same size in both fraction names. - Look for a way to group all of the sixth-size parts into larger equal groups.

Solution

1. The model has \(4\) of \(6\) equal parts shaded, so it shows \(\frac{4}{6}\). 2. Eli's reason is not correct: the model leaves \(2\) sixths unshaded, while \(\frac{2}{3}\) leaves \(1\) third unshaded. 3. Group the \(6\) equal parts into \(3\) equal pairs. The \(4\) shaded sixths form \(2\) complete pairs. 4. Therefore, \(\frac{4}{6}=\frac{2}{3}\), but the correct reason is the equal regrouping, not simply that “two parts” are involved.

Answer

Eli's explanation is not correct because the parts being counted are different sizes. A correct explanation is that the \(6\) equal parts can be grouped into \(3\) equal pairs, with \(2\) pairs shaded, so \(\frac{4}{6}=\frac{2}{3}\).
5401763
The same transparent cover is placed in the same position over two same-size grids. Use the models to name the covered fraction in each grid and explain why the fractions are equivalent.
Figure for problem 540176

Hints

- Count the equal parts covered in each grid. - Focus on the physical region covered, not only on the number of pieces. - Explain why splitting each column into smaller equal parts does not change the covered area.

Solution

1. In grid a), the cover spans \(2\) of \(3\) equal columns, so it covers \(\frac{2}{3}\) of the whole. 2. In grid b), each column is split into \(2\) equal cells. The same cover spans \(4\) of the \(6\) equal cells, so it covers \(\frac{4}{6}\). 3. The cover has the same size and position on two same-size wholes, so it covers the same amount in both grids. 4. Therefore, \(\frac{2}{3}=\frac{4}{6}\).

Answer

The grids show \(\frac{2}{3}\) and \(\frac{4}{6}\). The same cover occupies the same region of each same-size whole, so \(\frac{2}{3}=\frac{4}{6}\).
5401873
Use the three same-size models. A student has explained that model a) is equivalent to model b), and model b) is equivalent to model c). Explain why this is enough to conclude that models a) and c) show equivalent fractions. Write the resulting equality.
Figure for problem 540187

Hints

- Read the fraction shown by each model. - Track which model is known to match model b). - If two amounts each match the same amount, decide what that tells you about those two amounts.

Solution

1. The three models show \(\frac{1}{2}\), \(\frac{2}{4}\), and \(\frac{4}{8}\). 2. Models a) and b) shade the same amount of a same-size whole. 3. Models b) and c) also shade the same amount of a same-size whole. 4. Therefore, models a) and c) both match the same shaded amount, so \(\frac{1}{2}=\frac{4}{8}\).

Answer

Both \(\frac{1}{2}\) and \(\frac{4}{8}\) represent the same shaded amount as \(\frac{2}{4}\). Therefore, \(\frac{1}{2}=\frac{4}{8}\).
5402023
Each bar represents the same-size whole. Bars a) and b) together form one amount. Bars c) and d) together form another amount. Use the models to write each amount as a fraction. Then decide whether the two fractions are equivalent and explain your reasoning.
Figure for problem 540202

Hints

- Count the shaded unit-fraction parts across each pair of bars. - Compare the partially shaded second bar in each pair. - Think about how many fourth-size pieces cover the same amount as one half-size piece.

Solution

1. Bars a) and b) contain \(3\) shaded halves altogether, so they show \(\frac{3}{2}\). 2. Bars c) and d) contain \(6\) shaded fourths altogether, so they show \(\frac{6}{4}\). 3. In each pair, one whole bar is fully shaded and half of the second bar is shaded. Two fourths cover the same amount as one half. 4. Therefore, the two amounts are equal and \(\frac{3}{2}=\frac{6}{4}\).

Answer

The models show \(\frac{3}{2}\) and \(\frac{6}{4}\). They are equivalent because both show one whole plus the same half-whole amount, so \(\frac{3}{2}=\frac{6}{4}\).
5402153
Use the number line. Name point \(X\) in sixths. Then explain why the same point can also be named with denominator \(3\).
Figure for problem 540215

Hints

- Count the small equal spaces from \(0\) to \(1\) to identify the unit fraction. - Count how many of those spaces reach point \(X\). - Think about how the small spaces can be grouped equally to name the same distance in thirds.

Solution

1. From \(0\) to \(1\), the number line has \(6\) equal spaces, so each small space is one sixth. 2. Point \(X\) is \(8\) small spaces from \(0\), so \(X=\frac{8}{6}\). 3. Two sixth-size spaces have the same length as one third-size space. Thus, \(8\) sixths make \(4\) thirds. 4. Therefore, \(X=\frac{8}{6}=\frac{4}{3}\).

Answer

\(X=\frac{8}{6}=\frac{4}{3}\). Two sixth-size spaces make one third-size space, so 8 sixths make 4 thirds. Therefore, \(\frac{8}{6}\) and \(\frac{4}{3}\) name the same point.
5402213
Use models a) and b). Write the fraction shown by each model, then explain why the two fractions are equivalent using the sizes and counts of the equal parts.
Figure for problem 540221

Hints

- Count the shaded unit-fraction parts in each model. - Compare the size of one part in model a) with the smaller parts in model b). - Explain what changes in the part count and what stays the same in the total amount.

Solution

1. Model a) shows \(5\) half-size parts, so it represents \(\frac{5}{2}\). 2. Model b) shows \(10\) fourth-size parts, so it represents \(\frac{10}{4}\). 3. Each half-size part has the same size as \(2\) fourth-size parts. Five halves therefore have the same size as \(10\) fourths. 4. Thus, \(\frac{5}{2}=\frac{10}{4}\).

Answer

Model a) shows \(\frac{5}{2}\), and model b) shows \(\frac{10}{4}\). Every half can be split into two fourths, so \(\frac{5}{2}=\frac{10}{4}\).
5401253
Use the two same-size bar models. Both have exactly one unshaded part. Explain why that does not make their shaded fractions equivalent.
Figure for problem 540125

Hints

- Count the total equal parts in each same-size bar. - One unshaded piece does not necessarily have the same size in two different partitions. - Compare the unshaded fractions before deciding whether the shaded amounts match.

Solution

1. Model a) has \(3\) of \(4\) equal parts shaded, so its unshaded part is \(\frac{1}{4}\) of the whole. 2. Model b) has \(5\) of \(6\) equal parts shaded, so its unshaded part is \(\frac{1}{6}\) of the whole. 3. One fourth is larger than one sixth, so the models leave different amounts unshaded. 4. Therefore, the shaded fractions \(\frac{3}{4}\) and \(\frac{5}{6}\) are not equivalent.

Answer

The single unshaded parts are different sizes. One model leaves \(\frac{1}{4}\) unshaded and the other leaves \(\frac{1}{6}\), so the shaded fractions are not equivalent.
5401643
A bar starts with \(2\) of \(3\) equal parts shaded. Method A splits all three parts into \(2\) equal smaller parts. Method B splits only the shaded parts. Which method makes a valid equivalent-fraction model, and why?

Hints

- Check whether each method splits every original part in the same way. - A fraction model must divide the whole into equal parts. - Count the new equal parts and shaded parts in Method A.

Solution

1. Method A creates \(6\) equal parts across the whole bar, with \(4\) shaded, so it shows \(\frac{4}{6}=\frac{2}{3}\). 2. Method B creates smaller shaded pieces but leaves one larger unshaded piece. 3. Method B does not divide the whole into equal parts. 4. Only Method A makes a valid equivalent-fraction model.

Answer

Method A is valid because it divides the entire whole into \(6\) equal parts and shows \(\frac{2}{3}=\frac{4}{6}\). Method B creates unequal parts.
5402093
Use the eighths strip. A student removes only the divider between the two shaded parts and says the strip now proves that the shaded amount can be named as one fourth. Explain what else must happen to make a valid fourths model.
Figure for problem 540209

Hints

- First read the shaded fraction from the strip. - After the proposed change, check whether every visible part of the whole would have the same size. - A valid new denominator must describe equal parts across the entire whole, not only the shaded region.

Solution

1. The strip has \(2\) of \(8\) equal parts shaded, so it begins as \(\frac{2}{8}\). 2. Removing only the divider between the shaded parts creates one larger shaded piece but leaves six separate unshaded eighths. 3. The visible pieces are then unequal, so they do not form fourths. Every pair of eighths across the whole strip must be grouped in the same way. 4. Then the whole has \(4\) equal parts and \(1\) is shaded, showing \(\frac{2}{8}=\frac{1}{4}\).

Answer

The student must group every pair of eighths across the entire strip, not only the shaded pair. Then the whole has \(4\) equal parts and \(1\) is shaded, so \(\frac{2}{8}=\frac{1}{4}\).
5540473
A bar originally has \(2\) of \(3\) equal sections shaded. Two students try to split the sections into smaller parts without changing the shaded amount. Their results are shown in diagrams a) and b). Which diagram is a valid equivalent-fraction model with denominator \(6\)? Explain what is wrong with the other diagram.
Figure for problem 554047

Hints

- Check whether every visible part in each final bar has the same width. - A denominator of \(6\) must describe six equal parts of the entire whole. - The shaded amount may stay the same even when the new partition is not a valid fraction partition.

Solution

1. Diagram a) divides the entire bar into \(6\) equal parts. 2. Four of those \(6\) equal parts are shaded, so diagram a) shows \(\frac{4}{6}\), the same shaded amount as \(\frac{2}{3}\). 3. Diagram b) splits only the originally shaded thirds. Its unshaded section remains twice as wide as each smaller shaded section. 4. Because diagram b) does not divide the whole into equal parts, it cannot be read as sixths. Diagram a) is the valid model.

Answer

Diagram a) is valid and shows \(\frac{2}{3}=\frac{4}{6}\). Diagram b) is invalid because its visible parts are not all equal.

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