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Maths Puzzle
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A group of 630 children is arranged in a row 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
Read Solution (Total 2)
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- solve through options
we know s = n/2 [2a+(n-1)d)
here common difference is -3
put n=4
here sum s = 630
so, 630=4/2[2a+(4-1)(-3)]
630=4a-18
4a=648
a= 648/4=162
so arrangement be 162+159+156+153=630
so number of rows is 4
- 10 years agoHelpfull: Yes(2) No(1)
- Number of row=6 is not possible
Sum of arithmetic series whose difference is d is given as ;S=n/2*(2a+(n-1)*d)
a=(2s/n-(n-1)*d)/2
d=3 and S=630 are constant;
if n=3; a=207; Hence, 207+210+213=630. Similarily;
n=4; a=153; Hence. 153+156+159+162=630.
..............
n=6; a=195/2 NOT POSSIBLE - 10 years agoHelpfull: Yes(2) No(1)
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