A machine that produces stampings for car engines is not working properly and prducing 15% defectives. The defective and non defective stampins proceed from the machine on a random manner. If 4 stampings are randomly collected, find
1. The probability that almost 2 are defective
2. Mean
3. variance and standard deviation
An Electrical firm manufactures light bulbs that have a lifespan that is normally distributed with a mean 900 hours and standard deviation of 50 hours. out of 250 bulbs, about how many bulbs will have lifespan between 970 and 950 hours.