# Question 7640c

Jul 22, 2017

Nine

#### Explanation:

23 years = 23 × 365 years = 23 × 365 × 24 × 3600 seconds

23 years = 725328000 seconds = 7.25328 × 10⁸ seconds

Order of magnitude of a×10^b# when $a > 5$ is $b + 1$

Therefore order of magnitude of 7.25328 × 10⁸ seconds is 8 + 1 = 9