Question
If 2515 is divided by 13, the reminder is _________.

Answer

If 2515 is divided by 13, the reminder is 12.
Solution:
$25^{15}=(26-1)^{15}$ $=\ ^{15}\text{C}_0{26}^{15}-\ ^{15}\text{C}_126^{14}+...+\ ^{15}\text{C}_{14}26-\ ^{15}\text{C}_{15}$
$=(^{15}\text{C}_026^{15}-\ ^{15}\text{C}_126^{14}+...+\ ^{15}\text{C}_{14}26-13)+12$
Clearly, when 2515 is divided by 13, then remainder will be 12.

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