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.