Question

A box contains 100 bulbs 20 of which are defective. 10 bulbs are selected for inspection. Find the probability that: i. all 10 are defective ii. all 10 are good ii. at least one is defective iv. none3 is defective. Select the correct answer from above options

Answer 1

total no of bulbs=100. total no of defective bulbs =20. we have take out 10 bulbs, therefore total possible outcomes is .100C10 1. if all the 10 are defective means taken out from 20 defective bulbs i.e possible outcome is .20C10 therefore probability isp= .20C10 .100C10 2.if all the 10 are good that is taken out from rest of the 80 which are good bulbs i.e possible outcome is .80C10 therefore robability is p= .80C10 .100C10 4.atleast one is defective means we have to find all the probabilities when one is defective ,2 is defective and 3 is defective so on .so find probility when none is defective i.e all are good which is p= .20C10 .100C10 therefore probability of atleast one defective is 1-p = 1- .20C10 .100C10