Olympiad Maths Prep

Track / Stage 4 / 246 of 340 #506 of 2000

Problem 506

AMC 12 late, AIME early
Number theory Difficulty 4.9 Find the answer

Subject 1. Determine the prime numbers a<b<ca<b<c that satisfy the relation

13a+65b+289c=6622 13 a+65 b+289 c=6622

Official solution

## Subject 1.

| The numbers a,b,ca, b, c cannot all be odd because 6622 is even. Therefore, either they are all even | 2p\mathbf{2 p} |
| or only one of them is even. | 1p\mathbf{1 p} |
| a=b=c=2a=b=c=2 does not satisfy the relation | 1p\mathbf{1 p} |
| since a<b<ca=2a<b<c \Rightarrow a=2 | |
| we get 65b+289c=659665 b+289 c=6596. The numbers 289 and 6596 have 17 as a common divisor 17\Rightarrow 17 is | |
| a divisor of 65b65 b and thus of bb. But bb is prime b=17\Rightarrow b=17 | 2p\mathbf{2 p} |
| Finally, c=19c=19. | 1p\mathbf{1 p} |

Source: NuminaMath-1.5, licensed Apache-2.0. Statement and solution reproduced as published; topic, difficulty and ordering added by this site.