Problem 3 · 2010 Math Kangaroo
Easy
Arithmetic & Operations
arithmetic-seriessum-constraint
Which number goes in the cell with the question mark if the sum of the numbers in both rows is equal?
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 2010 |
| 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | ? |
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Answer: C — 1910
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Hint 1 of 2
Add up the top row, including the 2010 on the end.
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Hint 2 of 2
The bottom row's known cells plus the missing one must reach the same total.
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Approach: equal-sum balance
- Top row: 1+2+...+10 = 55, plus 2010, giving 2065.
- Bottom row so far: 11+12+...+20 = 155.
- The missing cell must make 155 + ? = 2065, so ? = 1910.
Mark:
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