algebra
posted by Anna Swain .
The breaking strength (in pounds) of a certain new synthetic is normally distributed, with a mean of 166 and a variance of 4. The material is considered defective if the breaking strength is less than 160 pounds. What is the probability that a single, randomly selected piece of material will be defective? (Give the answer to two decimal places.

variance = 4, so standard deviation = 2 (because squareroot of 4 is 2)
160  166 = 6 = 3 standard deviation.
You take out a normal distribution table and you find out that a standard deviation of 3 or less happens only 0.13% of the time.
Answer : 0.13% 
Thanks a million!!!