Problem 11 · 2016 Math Kangaroo
Medium
Logic & Word Problems
sum-constraint
Mona, Asma and Nadja work in the same nursery. On each day from Monday to Friday exactly two of them are working. Mona works three times and Asma works four times per week. How many times does Nadja work per week?
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Answer: C — 3
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Hint 1 of 2
Each weekday exactly two of the three work, so add up all the work-days.
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Hint 2 of 2
Mona's 3 plus Asma's 4 plus Nadja's count must equal the total work-days.
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Approach: count the total worker-days
- Two people work each of the 5 days, so the week has \(2 \times 5 = 10\) worker-days in total.
- Mona fills 3 of them and Asma fills 4, which is 7 worker-days.
- Nadja fills the rest, \(10 - 7 = 3\) days, choice (C).
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