Question

Bob is falling down from a height. If he falls `x^2+5x` m in `x` seconds, how many seconds does it take him to fall `500` m?

Answer 1

It is 20s.

Explanation:

We need to solve the distance formula for
`x^2 + 5x=500`.

This is a quadratic:
`x^2 +5x-500=0`

We can factorise this as:
`(x+25)*(x-20)=0`

Hence `x=20s`