Question 71
MediumOriginal questionChairs set out in rows of 3 leave 2 over, and in rows of 5 leave 3 over. What is the least number of chairs?
Show the answer and explanation
CorrectNot quiteAnswer B
Correct answer: B
Explanation
We need and .
Numbers : 3, 8, 13, … The first that leaves 2 on division by 3 is 8.
Worth noting
23 works too but is not the least; solutions repeat every 15.
- Concept
- Two congruences together
- Typical timeTypical
- 90 s
- Your timeYours
- —
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Ten questions from Modulo Arithmetic & Congruence, at your own pace.