you need 18 computer memory chips to install in the motherbo

you need 18 computer memory chips to install in the motherboard of a microcomputer. your order 20 memory chips because you know that 10 percent of all chips are defective. what is the probability that your computer will work?

Solution

prob of finding defective = 0.1

probability that your computer will work = prob of finding 0 defective + prob of finding 1defective + prob of finding 2 defective

= 20C0 * 0.1⁰ * 0.9²⁰ + 20C0 * 0.1¹ * 0.9¹⁹ + 20C0 * 0.1² * 0.9¹⁸

= 0.1216 + 0.2702 + 0.2852

= 0.6769