A ball is thrown straight up. Its height, h(in metres), after t seconds is given by h=-5t^2+10t+2. To the nearest tenth of a second, when is the ball 6m above the ground?

Explain why there are two answers.

set h=6
rearrange the quadratic equation to get
5t^2 - 10t + 4=0

Solve using the formula, you should get two positive answers, one will represent the time for its upwards path, and the second the time on its downwards trip.