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What is the remainder when $7^{103}$ is divided by 25?

Competition practiceNumber System, HCF & LCM

A18
B7
C24
D43

Step-by-Step Solution

7^{2} = 49 \equiv - 1

(mod 25), so

7^{4} \equiv 1.103 = 4 \times 25 + 3

, hence

7^{103} \equiv 7^{3} = 343 \equiv 343 - 325 = 18

.

Answer: A) 18

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