Skip to main content
OlympiadHQ

Browse · MATH

Print

jmc

number theory senior

Problem

What is the least positive integer which when divided by 5 gives a remainder of 4, when divided by 6 gives a remainder of 5, when divided by 7 gives a remainder of 6, when divided by 8 gives a remainder of 7, when divided by 9 gives a remainder of 8, and when divided by 10 gives a remainder of 9?
Solution
Suppose that is a positive integer satisfying all the given conditions. Note that since gives a remainder of 4 when divided by 5, must be divisible by 5. Similarly, is also divisible by 6, 7, 8, 9, and 10. Thus the least possible value for is the least common multiple of 6, 7, 8, 9, and 10. Prime factorizing these numbers, we find that their least common multiple is . Thus the least possible value for is .
Final answer
2519