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M16-16

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Math Expert
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Joined: 02 Sep 2009
Posts: 49251
M16-16  [#permalink]

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New post 16 Sep 2014, 00:59
00:00
A
B
C
D
E

Difficulty:

  5% (low)

Question Stats:

84% (00:46) correct 16% (00:30) wrong based on 70 sessions

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Math Expert
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Posts: 49251
Re M16-16  [#permalink]

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New post 16 Sep 2014, 00:59
1
Intern
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Joined: 29 Sep 2016
Posts: 16
Location: United States
Concentration: Finance, Economics
GPA: 3.01
Re: M16-16  [#permalink]

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New post 06 Nov 2016, 15:44
1
Referencing The GMAT Club Math Book (pg.13)

To find the n of last digits of the product = product of n digits of the integers.

By looking at the answer choices, the answers very at the hundred digit places.
A = 866, B =956, C=856, D= 986, E = 996.

Thus we want to find the last 3 digits of the product in order to find the answer.

8988 * 12 = 10856. (note that it's not necessary for you to calculate beyond 856). Thus the only answer that contains 856 is C.
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Re: M16-16  [#permalink]

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New post 09 Mar 2017, 08:24
2
I think the official answer here is the best way of looking at the problem.

When I first approached this question, however, I didn't notice that 8988 could be re-written as (9000-12).

I was still able to solve the question in under 1:30 seconds, though. I figured rather than trying to spend 30 seconds trying to think of a way to solve this, I could actually just multiply the two numbers quickly on paper. And quickly noticed I didn't have to solve the whole thing to find the answer.

8988
*
9012
------
17976
89880
000
0000
------
xx856

After adding the last two digits (76+80) I noticed the answer must end in 56. This eliminated everything but B and C. Then adding the last three digits 976+880+000 shows the answer must be 856.

I am not posting this because this is the most efficient way, but another way of looking at the problem because sometimes instead of losing precious time trying to find the easiest way to do something it might be quicker to just grind it out.
Re: M16-16 &nbs [#permalink] 09 Mar 2017, 08:24
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