Problem 10 · 2009 Math Kangaroo
Medium
Geometry & Measurement
gridcareful-counting
Peter shared a bar of chocolate. First he broke off a row with five pieces for his brother. Then he broke off a column with 7 pieces for his sister. How many pieces were there in the entire bar of chocolate?
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Answer: D — 40
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Hint 1 of 2
A 'row of five' tells you how many columns the bar has; a 'column of seven' tells you how many rows.
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Hint 2 of 2
Be careful: the column he breaks off is from what is LEFT after the first row is gone.
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Approach: recover the grid dimensions, then multiply
- A row holds 5 pieces, so the bar is 5 columns wide.
- After removing that row, a full column still has 7 pieces, so the bar has 7 + 1 = 8 rows.
- The whole bar is 8 rows × 5 columns = 40 pieces.
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