A rainwater tank begins with \(120\,\text{L}\). Over the next five days, \(30\,\text{L}\) is added, \(10\,\text{L}\) is removed, \(40\,\text{L}\) is added, \(20\,\text{L}\) is removed, and \(50\,\text{L}\) is added.
Lucas writes two expressions for the amount of water after these changes:
Expression 1: \(120+30-10+40-20+50\)
Expression 2: \(120+(30+40+50)-(10+20)\)
a) Evaluate both expressions.
b) Explain what the two grouped expressions in Expression 2 represent in this situation.
Hints
- Match the positive changes with water added and the negative changes with water removed.
- Compare the terms being added with the terms being subtracted in the two expressions.
- In Expression 2, interpret each grouped sum as one combined quantity before evaluating.
Solution
1. For part a), Expression 1 gives \(120+30-10+40-20+50=210\,\text{L}\). Expression 2 gives \(120+120-30=210\,\text{L}\). Both expressions have the same value.
2. For part b), \((30+40+50)\) represents the total amount of water added, and \((10+20)\) represents the total amount of water removed.
Answer
a) Both expressions equal \(210\,\text{L}\).
b) \((30+40+50)\) is the total water added, and \((10+20)\) is the total water removed.