Question
The remainder when $3^21$ is divided by 5 is
Answer: Option D
Answer: (d)$3^1 = 3; 3^2 = 9; 3^3 = 27; 3^4 = 81; 3^5$ = 243 i.e. unit’s digit is repeated after index 4. Remainder after dividing 21 by 4 = 1 ∴ Unit’s digit in the expansion of $(3)^21$ = 3 ∴ Remainder after dividing by 5 = 3
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Answer: (d)$3^1 = 3; 3^2 = 9; 3^3 = 27; 3^4 = 81; 3^5$ = 243 i.e. unit’s digit is repeated after index 4. Remainder after dividing 21 by 4 = 1 ∴ Unit’s digit in the expansion of $(3)^21$ = 3 ∴ Remainder after dividing by 5 = 3
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