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Properties of number question from GMAT Review 12th Edition [#permalink]
18 Apr 2010, 22:54

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.

Re: Properties of number question from GMAT Review 12th Edition [#permalink]
19 Apr 2010, 07:15

If you do the calculation using estimation and rounding, it's actually not too bad.

Yes, there are some difficult questions in the diagnostic test, and they get progressively more difficult throughout the section. They seem to be more "model" GMAT questions than the ones that actually appear on the exam. In order words, they lend themselves to solving easily using methods and tricks. That's not always true on the exam itself.

Re: Properties of number question from GMAT Review 12th Edition [#permalink]
19 Apr 2010, 22:16

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