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Find the remainder when \(2^{31}\) is divided by 5.

  • A.1
  • B.2
  • C.3
  • D.4

Answer: C

We look at the pattern of remainders of powers of 2 when divided by 5.

\(2^1 \div 5 \rightarrow rem=2\)

\(2^2 \div 5 \rightarrow rem=4\)

\(2^3 \div 5 \rightarrow rem=3\)

\(2^4 \div 5 \rightarrow rem=1\)

The cycle of remainders is (2, 4, 3, 1), which has a length of 4. To find the remainder of \(2^{31}\), we find the remainder of the power when divided by the cycle length: \(31 \div 4 \rightarrow rem=3\). The required remainder is the 3rd in the cycle, which is 3.

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