A company makes batteries with an average life span of 300 hours with a standard deviation of 75 hours. Assuming the distribution is approximated by a normal curve fine the probability that the battery will last:(give 4 decimal places for each answer)

Question

a. Less than 250 hours

b. Between 225 and 375 hours

c. More than 400 hours

I know the formula. X-mean/SD. I need help checking my answers!

Answer 1

this site should help:

http://davidmlane.com/hyperstat/z_table.html