OG上一道小小数学题

小橘子

15. The product of all the prime numbers less than 20 is
closest to which of the following powers of 10 ?
(A) 10^9
(B) 10^8
(C) 10^7
(D) 10^6
(E) 10^5


答案C
OG上有这道题，答案是直接乘出来 ，再得到。
2 × 3 × 5 × 7 × 11 × 13 × 17 × 19 = 9,699,690).
Th is is closest to 10,000,000 = 107
(10 × 10 × 10 × 10 × 10 × 10 × 10 = 10,000,000).



有没有简便的，这样干乘不是很浪费时间
大家谁有简便方法撒？？？多谢！