Question

$7^{81}+7^{82}+7^{83}$ is completely divisible by which of the following?

• A. 76
• B. 38
• C. 399
• D. 153

Answer 1

Answer:

C. 399

Given that,

781 + 782 + 783

⇒ 781 ( 1 + 7 + 7²)

⇒ 781 (57)

⇒ 780 $\times$ 7 $\times$ (57)

⇒ 780 $\times$ 399

∴ 781 + 782 + 783 is completely divisible by 399.