5^99 is divided by 13 then remainder is
We should try and reduce the numerator in this case. Let us have a look at the method below.
Remainder [5^99 / 13]
= Remainder [5*5^98 / 13]
= Remainder [5*25^49 / 13]
= Remainder [5*(-1)^49 / 13]
= Remainder [(-5) / 13]
= 8
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It simply follows a cycle..
5^1 / 13 - Remainder is 5
5^2 / 13 - Remainder is 12
5^3 / 13 - Remainder is 8
5^4 / 13 - Remainder is 1
5^5 / 13 - Remainder is 5
5^6 / 13 - Remainder is 12
.......... and so on. Hence,
5^96 / 13 - Remainder is 1
5^97 / 13 - Remainder is 5
5^98 / 13 - Remainder is 12
5^99 / 13 - Remainder is 8
Answer : 8