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Re: Strategy Pages (by ETS) - Value?
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27 Jan 2019, 09:37
Hi jjsomanytabs.
While you have gotten the answer to your specific question, it seems worth adding that while learning certain GRE quant tips or tricks can be helpful, strategies and tricks can take you only so far. You also need to ensure that you learn and understand the quant concepts on which GRE quant questions are based. By doing so, you will learn the RIGHT WAY to attack and efficiently solve problems, and thus, in many cases you won’t have to rely on trick. And, even when you do rely on strategies, you will apply them more effectively if you understand the math that underlies what you are doing.
Let me provide you with an example:
14! is equal to which of the following?
(A) 87,178,291,200
(B) 88,180,293,207
(C) 89,181,294,209
(D) 90,000,000,003
(E) 91,114,114,114
Upon seeing this question, what is the first thing that comes to mind? Grabbing a calculator to add up the values in the expression? Or are you able to quickly recognize that using the “5 x 2 pair rule” will allow you to efficiently attack the problem?
Solution:
14! = 14 × 13 × 12 × 11 × 10 × 9 × 8 × 7 × 6 × 5 × 4 × 3 × 2 × 1.
Notice that there is at least one (5 × 2) pair contained in the product of these numbers. It follows that the units digit must be a zero. The only number with zero as the units digit is 87,178,291,200.
Answer: A
Although this is just one example of many, you see that by understanding the rule of trailing zeros (not necessarily relying on a trick or hack), you would have been able to easily solve this question, right?