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The last one is trivial, too. Is 8 x 8 + 7 x 8 + 89 = 209 divisible by 77? Nope. Is 18 x 18 + 7 x 18 + 89 = 539 divisible by 77? Yes, gives 7, solved it. This i
by danbruc 11y ago
The last one is trivial, too. Is 8 x 8 + 7 x 8 + 89 = 209 divisible by 77? Nope. Is 18 x 18 + 7 x 18 + 89 = 539 divisible by 77? Yes, gives 7, solved it. This isn't even worth trying to look for a more analytical solution.
- OscarCunningham 11y agoBut since I didn't know in advance that the solution would be one of the smaller possible answers it was faster in expectation to solve the problem using the given method.
- tromp 11y agoThe question at the actual competition was slightly more subtle: it asked for m modulo 10. So it would have taken rather more tries to find 18...