Question

If $Log_{10}7=0.8451$ then the position of the first significant figure of $7^{-20}$ is

• A. 16
• B. 17
• C. 20
• D. 15

Answer 1

Answer: (B)

17

Answer 2

Let $x=7^{-20}$
$\log _{10} x=-20 \log _{10} 7$
$=-20(0.8451)$
$=-16.902$
Hence, the first significant figure is $17 .$