Question

Please help!! I don’t know how to solve this. Which one is the digit of the units in 3^81:

Answer 1

Solution:

• 3⁸¹ = 3⁹ ⁺ ⁹ ⁺ ⁹ ⁺ ⁹ ⁺ ⁹ ⁺ ⁹ ⁺ ⁹ ⁺ ⁹ ⁺ ⁹ ⁺ ⁹
• 3⁸¹ = 3⁹ x 3⁹ x 3⁹ x 3⁹ x 3⁹ x 3⁹ x 3⁹ x 3⁹ x 3⁹
• 3⁹ = 19683 [Using Calculator]

This means that the Unit digit of 19683 is 3. For each number, multiply the unit's digit of 3⁹.

• 3 x 3 x 3 x 3 x 3 x 3 x 3 x 3 x 3
• => 19683
• => Unit digit of 3⁸¹ = 3

Option A is correct.