In an auditorium, seats are arranged in rows and columns. The number of rows were equal to the number of seats in each row. When the number of rows were doubled and the number of seats in each row was reduced by 10, the total number of seats increased by 300.

How many number of rows are there in the original arrangement?

Options

A. 20
B. 40
C. 10
D. 30

Answer

D

Explanation

We have `" "x^(2)-20x-300=0`
`x^(2)-30x+10x-300=0`
`x(x-30)+10(x-30)=0`
`(x-30)(x+10)=0`
`x=30,-10`
Thus (d) is correct option.