What is the probability that the random quadratic expression x^2+2x-15 will be more than 0 if x is chosen randomly over the interval (-10,10)

Question

What is the probability that the random quadratic expression x^2+2x-15 will be more than 0 if x is chosen randomly over the interval (-10,10)

Answer 1

x^2 +2x -15 = (x+5)(x-3), -5 and +3 are the x intercepts, between them the quadratic is negative

-10 to -5 it's positive, 3 to 10 also positive

that's 12/20 = 3/5 = 60% chance of positive on that interval