thanatoz wrote:

Question 15 on GMAT Review Diagnostic Test

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

The solution in the book makes you CALCULATE the exact number then compare it to the answers, very time consuming without a calculator.

BTW - Are questions in the diagnostic test harder than normal GMAT questions? Or are they the hardest in each category? I find them so much harder than the regular CAT test.

this one can be done easily as shown below.

the prime numbers <20 are 2,3,5,7,11,13,17,19

taking the product of two at a time, we get 6, 35, 77, 221 and 19

on further applying this method of rounding and approximating, we see that the product nears 10^7

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CHEERS

fivezero7