I am not certain if you use the standard notation that variance = (standard deviation)^2
if so , then SD = 3
I make use of this webpage for routine standard deviation problems
http://davidmlane.com/hyperstat/z_table.html
enter the mean of 169 and sd of 3, then click the "below" button and enter 163
I got a probability of.002275
If you meant your sd to be 9, make the necessary changes in your input
The breaking strength (in pounds) of a certain new synthetic is normally distributed, with a mean of 169 and a variance of 9. The material is considered defective if the breaking strength is less than 163 pounds. What is the probability that a single, randomly selected piece of material will be defective? (Give the answer to two decimal places.)
1 answer
1 answer