# Basic probability question

1. Nov 24, 2004

### semidevil

I dont remember the exact story problem, but it goes something like this.

You are suppose to make a pin that is 6 cm long. Unfortunately, the machine will produce pins that 6 + y cm long. where 0 <= y <= 2, and the function f(y) = K(y + y^2).

if the pin is more then 7 cm long, then it is unusable. Find the proportion that is produced that will be unusable.

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ok, so if y = 0, or y = 1, then it is fine, and if y = 2, then it is unusable.

so can I just integrate from 0 to 1 of f(y), and then subtract from 1, to get the answer?

the book says the answer is 23/28....but I dont know how it got that.

2. Nov 24, 2004

### Tom Mattson

Staff Emeritus
Not quite. It should read: If 0<=y<=1, then it is fine, and if 1<y<=2, then it is unusable.

Yes, but first, you have to find K. To get it you have to normalize the probability distribution by integrating f(y) over the sample space and setting it equal to 1. This will allow you to solve for K. Then you can do what you have proposed above.