Question 95
MediumOriginal questionA school numbers its 60 students from 1 to 60 and puts each in a house by the remainder of the roll number on division by 5: remainder 1 is Red, 2 Blue, 3 Green, 4 Yellow and 0 White.
A Blue student and a Yellow student add their roll numbers. Which house matches the sum?
Show the answer and explanation
CorrectNot quiteAnswer C
Correct answer: C
Explanation
In classes modulo 5: .
Remainder 1 is Red, whatever the two roll numbers are.
Worth noting
The sum can be checked with any pair, such as or : both leave 1.
- Concept
- Adding residue classes
- Typical timeTypical
- 120 s
- Your timeYours
- —
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