A group of 260 children are seated in n rows for a group photo session. Each row contains three less children than the row in front of it. Which of the following number of rows is not possible?
Explanation
Let no of children be x, x + 3, x + 6, x + 9, x + 12, x + 15...... Present in Rows R1 ,R2, R3, R4, R5, R6 .......
respectively
Putting R = 3, 4, 5 and 6
You have to check this question by option method
We see that when R = 3
x + x + 3 + x + 6 = 630
3x + 9 = 630
3x = 639
x = 213 (possible)
Similarly for n = 4
x+(x–3)+(x–6)+(x−9)=630
4x–18=630
⇒ x = 162
Similarly for n = 5
(4x–18)+(x−12)=630
5x–30=630
x=120
Again possible.
We see that when R = 6
x + x + 3 + x + 6 + x + 9 + x + 12 + x + 15 = 630
6x + 45 = 630
6x = 585
x = 97.5
then x is not an integer. So R = 6 does not satisfies.
