Number System - Last Digit of Power

CAT 1998 Slot 1 · QA · Easy · Number System

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What is the digit in the unit's place of 2512^{51}?

  1. A.

    2

  2. B.

    8

  3. C.

    1

  4. D.

    4

Answer

B

Explanation

Powers of 2 have a cyclicity of 4 in unit digits: 2, 4, 8, 6. 51(mod4)=351 \pmod 4 = 3. Therefore, the unit digit is 23=82^3 = 8.

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