The average US monthly cable bill in 2009 was 75 according t

The average US monthly cable bill in 2009 was $75 according to Centris, a marketing research firm. Assume monthly cable bills follow a normal distribution with a standard deviation of $9.50. What is the probability that a randomly selected bill will be less than $70?

Solution

P( x < 70)

P( z < [70-75] / 9.50 )

P( z < -0.53) = 0.2981