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31 Dec 2017, 14:23
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A
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
25%
(medium)
Question Stats:
80% (02:11) correct
20%
(02:41)
wrong
based on 198
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What is the least common multiple of 18,120, 216, and 1080?
A. 1,080
B. 19,440
C. 38,680
D. 38,860
E. 38,880
A. 1,080
B. 19,440
C. 38,680
D. 38,860
E. 38,880
31 Dec 2017, 14:41
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Bunuel
What is the least common multiple of 18,120, 216, and 1080?
A. 1,080
B. 19,440
C. 38,680
D. 38,860
E. 38,880
A. 1,080
B. 19,440
C. 38,680
D. 38,860
E. 38,880
To answer a question involving least common multiples it is usually helpful to look at prime factorizations.
This is a Precise approach.
18 factors into 3*3*2
120 factors into 12*10 = 2*2*3*5*2
216 factors into 2*108 = 2*3*36 = 2*3*4*9 = (2*2*2)*(3*3*3)
1080 factors into 10*108 = 10*(2*2*2)*(3*3*3)=(2*2*2*2)*(3*3*3)*5
The least common multiple involves the prime factors of all of the above.
Therefore, we need to count the largest number of 2's, 3's and 5's in the above numbers.
1080 has four 2's, 216 and 1080 have three 3's and 120, 1080 have one 5.
Therefore the least common multiple has four 2's, three 3's and one 5.
These are exactly the factors of 1080!
Therefore our answer is (A)
ramblers
Joined: 21 Aug 2017
Last visit: 19 Oct 2018
Posts: 67
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Given Kudos: 38
Location: United States
Schools: Oxford"20 (A)
GMAT 1: 700 Q43 V42
15 Feb 2018, 19:27
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Is there a quicker way than factoring all of them? Should I have known that those were all factors of 1080?
Maybe I just need to speed up my factoring, but this one took me a touch over 3 minutes.
Maybe I just need to speed up my factoring, but this one took me a touch over 3 minutes.
