Civil Services Prep

Prelims 2026 · CSAT / Quantitative Aptitude · Question 42

The digit in the unit place of the number 6^129 × 7^307 is<br/>

  1. 2
  2. 4
  3. 8
  4. 6

Answer

8

The unit digit of 6^129 is always 6. For 7^n, unit digits cycle as 7, 9, 3, 1 with period 4. Since 307 mod 4 = 3, the unit digit of 7^307 is 3. Therefore the unit digit of 6^129 × 7^307 is 6 × 3 = 18, i.e. 8.

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