The same digit fills all three boxes:
\(\frac{\square}{10}+\frac{\square}{100}+\frac{\square}{100}\).
a) List the digits that make the sum less than \(1\).
b) List the digits that make the sum greater than \(1\).
c) Does any digit make the sum exactly \(1\)?
Hints
- Use the same digit in all three boxes.
- Try values near the point where the total changes from below one whole to above one whole.
- Once you know what happens for neighboring boundary digits, use the fact that increasing the shared digit increases every addend.
Solution
1. Test the largest likely value below one. With \(8\) in every box, the sum is \(\frac{8}{10}+\frac{8}{100}+\frac{8}{100}=\frac{96}{100}\), which is less than \(1\).
2. Every smaller digit gives a smaller sum, so digits \(0\) through \(8\) all make the sum less than \(1\).
3. With \(9\) in every box, the sum is \(\frac{90}{100}+\frac{9}{100}+\frac{9}{100}=\frac{108}{100}\), which is greater than \(1\).
4. The sum jumps from \(\frac{96}{100}\) at digit \(8\) to \(\frac{108}{100}\) at digit \(9\), so no digit makes exactly \(1\).
Answer
a) \(0,1,2,3,4,5,6,7,8\)
b) \(9\)
c) No.