Probabiity two components are unacceptable

The probability that a chip is manufactured to an acceptable standard is 0.73. A sample of 4 chips is picked at random from a large batch.

I have calculated that all are acceptable 0.73^4 and none are 0.27^4. How can I calculate more than two are?

I tried 0.73^2 but then that + 0.27^2 does not make 1. What to do?

Thanks.

Re: Probabiity two components are unacceptable

Quote:

Originally Posted by

**mark090480** The probability that a chip is manufactured to an acceptable standard is 0.73. A sample of 4 chips is picked at random from a large batch.

I have calculated that all are acceptable 0.73^4 and none are 0.27^4. How can I calculate **more than two are**?

$\displaystyle \sum\limits_{k = 3}^4 {\binom{4}{k}{{(.73)}^k}{{(.27)}^{4 - k}}} $

Re: Probabiity two components are unacceptable

In other words, $\displaystyle 4(.73)^3(.27)+ (.73)^4$!