The product of all positive even numbers less than or equal to 20 is closest to which of the following?  Choose the correct choice from the following options
A) 10^6
B) 10^7
C) 10^8
D) 10^9
E) 10^10
2 * 4 * 6 * 8 * 10 * 12 * 14 * 16 * 18 * 20   Replacing closest digits to 10 (6,8,12,14) with 10 and closest to 20 (16,18) with 20.   ==&gt;(2 * 4) * (10 * 10 * 10 * 10 * 10) * (20 * 20 * 20)   ==&gt;8 * (10^5) * (8 * 10^3)   ==&gt;64 * 10^8   ==&gt;64 is closest to 50   ==&gt;50 * 10^ 8   ==&gt;5 * 10^9   Answer 10^9
<result>D</result>
The product of all positive even numbers less than or equal to 20 is closest to which of the following?