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GATE 2023 EE – Question 9

General Aptitude · Quantitative Aptitude: Arithmetic and Number Computation · 2 marks · Multiple choice

The digit in the unit’s place of the product $3^{999}\times7^{1000}$ is _______.

  1. 7
  2. 1
  3. 3
  4. 9

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Show answer and explanation

Correct answer: (A) 7

Explanation

$3^{999}\times7^{1000}=(3\times7)^{999}\times7=21^{999}\times7$. $21^{999}$ ends in 1, so the product ends in $1\times7=7$.