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?
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