Problem 13 · 2022 Math Kangaroo
Medium
Logic & Word Problems
off-by-one
In a classroom the children sit in rows, with the same number of children in each row. In Robert’s row there are 2 children to his left and 3 children to his right. There are 2 rows in front of Robert and just 1 row behind him. How many children are in the class in total?
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Answer: E — 24
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Hint 1 of 2
Count the children in Robert's row including Robert himself.
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Hint 2 of 2
Then count the rows, again including Robert's own row.
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Approach: count one row and the number of rows, including Robert
- In Robert's row there are 2 to his left, Robert, and 3 to his right: 2+1+3 = 6 children per row.
- There are 2 rows in front, Robert's row, and 1 behind: 2+1+1 = 4 rows.
- Total children = 6 × 4 = 24.
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