# maths probability

The lifetime X of a bulb is a random variable with the probability density function:
f(x)=6[0.25-(x-1.5)^2] when 1<=x<=2
0 otherwise
X is measured in multiples of 1000 hrs. What is the probability that none of the three
bulbs in a traffic signal have to be replaced in the first 1500 hrs of their operation.

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