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Find the number of rows

Q.)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?
(I)3 (ii)4 (iii)5 (iv)6 (v)7
SOLUTION:
Let the number of students in the front row be x.
And no of rows=n.
Hence, the no of students in the next rows would be
(x-3), (x-6), (x-9), ………….and so on.
If n , i.e., no of rows be 3, then number of students
=x + (x-3) +(x-6) =630

=>3x = 639 =>x=213
Likewise if n=4
x + (x-3) +(x-6) +(x-9) =630
=>x=162
Likewise if n=5
x + (x-3) +(x-6) +(x-9) +(x-12)=630
=>x=132
If n=6, then
6x = 675
So, n=6 is not possible.
Option(iv)

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