A firm selling type writers knows that four of its 100 type writers will not return properly and that five different ones have a defective key.If none of the other type writers has a defect,what is the probability of a buyer selecting a defective typewriter from this group of 100?
4 return defects+5 key defects=9 defects total in this batch of 100.
So you have 9 in 100 chance to get a defective typewriter or 9% chance.