Suppose the probability distribution function of the weight of a packet of rice is

f(x)={2, 49.75<x<50.25
{0, elsewhere

a)Determine the probability that a packet weighs more than 50 pounds.
b)How much rise is contained in 90%of all packets?

This looks like a uniform distribution.

Uniform distributions are easy because they are modeled by a rectangle.

Since x ranges from 49.75 to 50.25, we want the probability the rice is between 50 and 50.25. 50 is in the middle. That should give an idea what the probability is.

P(x>50)=2(50.25-50)

or, we can integrate and get the same result.

P(x>50)=2\int_{50}^{50.25}dx

OK,thank you for your answer!I'm so appreciate it><but how about the question (b)?