The product of all 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
Is there an easier way than actually having to lay out all the prime numbers and multiplying them and then comparing it to the answer choices?
My initial approach: Lay out all the prime numbers under 20 -- , 2, 3, 5, 7, 11, 13, 17, 19 -- and then visually see if I can turn each number into a 10 (i.e. averaging). After that, I estimated and the answer I got was 10^8.
The actual answer is (C) 10^7
(A) 10^9
(B) 10^8
(C) 10^7
(D) 10^6
(E) 10^5
Is there an easier way than actually having to lay out all the prime numbers and multiplying them and then comparing it to the answer choices?
My initial approach: Lay out all the prime numbers under 20 -- , 2, 3, 5, 7, 11, 13, 17, 19 -- and then visually see if I can turn each number into a 10 (i.e. averaging). After that, I estimated and the answer I got was 10^8.
The actual answer is (C) 10^7
Last edited by Emawk on Thu Dec 04, 2008 7:36 am, edited 1 time in total.
