Problem 15 · 2011 Math Kangaroo
Hard
Arithmetic & Operations
work-backward
Paul wanted to multiply a whole number by 301, but forgot to include the zero and multiplied by 31 instead. His answer was 372. What should his answer have been?
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Answer: B — 3612
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Hint 1 of 2
Use the wrong answer to recover the original whole number.
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Hint 2 of 2
Then multiply that number by 301 as he intended.
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Approach: undo the wrong multiplication, then redo it right
- He multiplied by 31 and got 372, so the number is 372 ÷ 31 = 12.
- The correct product is 12 × 301 = 3612.
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