Question

Find the last digit of 23⁷²⁹ × 78⁹⁰⁰
1. 7
2. 3
3. 0
4. 8

Answer 1

Correct Answer - Option 4 : 8

Given:

Last digit of 23⁷²⁹ × 78⁹⁰⁰

Calculation:

⇒ 23⁷²⁹ = (23)⁷²⁸ × 23 = (23²)³⁶⁴ × 23

The last digit of 23² is 9 and last digit of 23 = 3.

Similarly,

⇒ 78⁹⁰⁰ = (2 × 39)⁹⁰⁰ = (2¹⁰)⁹⁰ × (39²)⁴⁵⁰

The last digit of 2¹⁰ = 4 and last digit of 39² = 1

∴ Last digit of 23⁷²⁹ × 78⁹⁰⁰ = 9 × 3 × 4 × 1 = 108 which is 8.