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02 Aug 2015, 06:41
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D
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
95%
(hard)
Question Stats:
45% (02:24) correct
55%
(02:15)
wrong
based on 283
sessions
History
Date
Time
Result
Not Attempted Yet
A group of 630 children is arranged in rows for a group photograph session. Each row contains three fewer children than the row in front of it. What number of rows is not possible?
(A) 3
(B) 4
(C) 5
(D) 6
(E) 7
Source: GMAT notes (China Maths bible)
(A) 3
(B) 4
(C) 5
(D) 6
(E) 7
Source: GMAT notes (China Maths bible)
ENGRTOMBA2018
Joined: 20 Mar 2014
Last visit: 01 Dec 2021
Posts: 2,315
Given Kudos: 816
Concentration: Finance, Strategy
Schools: Kellogg '18 (M)
GMAT 1: 750 Q49 V44
GPA: 3.7
WE:Engineering (Aerospace and Defense)
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02 Aug 2015, 06:48
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GMATnavigator
Let n be the number of children in the least populated row. The subsequent rows will have n+3, n+6, n+9 ... etc children.
Start by POEing the options.
Option A, the distribution will be n, n+3, n+6 ---> n+n+3+n+6 = 630 --> n = Integer. Possible
Option B, the distribution will be n, n+3, n+6, n+9 ---> n+n+3+n+6+n+9 = 630 --> n = Integer. Possible
Option C, the distribution will be n, n+3, n+6, n+9, n+12 ---> n+n+3+n+6+n+9+ n+12 = 630 --> n = Integer. Possible
Option D, the distribution will be n, n+3, n+6, n+9, n+12, n+15 ---> n+n+3+n+6+n+9+ n+12+n+15 = 630 --> n \(\neq\) Integer. NOT POSSIBLE.
Option E, the distribution will be n, n+3, n+6, n+9, n+12, n+15, n+18 ---> n+n+3+n+6+n+9+ n+12+n+15+n+18 = 630 --> n = Integer. possible.
D is the correct answer.
02 Jul 2018, 09:24
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I would say this is 600 level.
Say row 1 has x children, then row 2 has x-3 and row 3 has x-6 and so forth. Hence, with plug and play, we get D as the answer since:
Row 1: x
Row 2: x - 3
Row 3: x - 6
Row 4: x - 9
Row 5: x - 12
Row 6: x- 15
This adds to 6x - 45 = 630 or 6x = 675. For a number to be divisible by 6, it must be divisible by both 2 and 3. 675 is not divisible by 2. All the rest of the answers result in an integer for x.
Say row 1 has x children, then row 2 has x-3 and row 3 has x-6 and so forth. Hence, with plug and play, we get D as the answer since:
Row 1: x
Row 2: x - 3
Row 3: x - 6
Row 4: x - 9
Row 5: x - 12
Row 6: x- 15
This adds to 6x - 45 = 630 or 6x = 675. For a number to be divisible by 6, it must be divisible by both 2 and 3. 675 is not divisible by 2. All the rest of the answers result in an integer for x.
