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12 May 2022, 07:00
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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:
82% (02:01) correct
18%
(02:57)
wrong
based on 56
sessions
History
Date
Time
Result
Not Attempted Yet
Five bells begin to toll together and toll at intervals of 36, 45, 72, 81 and 108 seconds. After what interval of time will they keep on tolling together?
(A) 3240 seconds
(B) 3200 seconds
(C) 3140 seconds
(D) 3080 seconds
(E) 3020 seconds
(A) 3240 seconds
(B) 3200 seconds
(C) 3140 seconds
(D) 3080 seconds
(E) 3020 seconds
12 May 2022, 13:52
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If a question looks like this much of a pain in the rear, there's probably a trick you can use. In this case, all of the intervals are multiples of 3, so we need an answer choice that is divisible by 3 (this is actually true even if only ONE of the intervals were divisible by 3). The rule for figuring out if a number is divisible by 3 is that the sum of its digits must be divisible by 3.
(A) 3240 3+2+4+0=9, which is divisible by 3.
(B) 3200 3+2+0+0=5, which is not divisible by 3. Wrong.
(C) 3140 3+1+4+0=8, which is not divisible by 3. Wrong.
(D) 3080 3+0+8+0=11, which is not divisible by 3. Wrong.
(E) 3020 3+0+2+0=5, which is not divisible by 3. Wrong.
We don't even need to test anything else since we've already proven four of the answer choices wrong.
Answer choice A.
(A) 3240 3+2+4+0=9, which is divisible by 3.
(B) 3200 3+2+0+0=5, which is not divisible by 3. Wrong.
(C) 3140 3+1+4+0=8, which is not divisible by 3. Wrong.
(D) 3080 3+0+8+0=11, which is not divisible by 3. Wrong.
(E) 3020 3+0+2+0=5, which is not divisible by 3. Wrong.
We don't even need to test anything else since we've already proven four of the answer choices wrong.
Answer choice A.
