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imc

number theory intermediate

Problem

What is the hundreds digit of
(A)
(B)
(C)
(D)
Solution
Since we know that To compute this, we use a clever application of the binomial theorem. In all of the other terms, the power of is greater than and so is equivalent to modulo which means we can ignore it. We have: Therefore, the hundreds digit is Side note: By Euler's Totient Theorem, for any relatively prime with 1000, so and . We can then proceed using the clever application of the Binomial Theorem, or we can just proceed with solution 6 from here.
Final answer
D