Question 10
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?
Solution
Let x be in the front row.
So no. of children in next rows will be x-3,x-6,x-9,x-12,x-15,x-18,x-21....
Suppose there are 6 rows, then the sum is equal to x + x-3 + x-6 + x-9 + x-12 + x-15 = 6x - 45
This sum is equal to 630.
=> 6x - 45 = 630 => 6x = 585
Here, x is not an integer.
Hence, there cannot be 6 rows.
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