To investigate the relationship between intracellular calcium and pulse-rates, researchers measured the free calcium concentration in the blood platelets of 38 people. They also measured the pulse rate for each person. Suppose the mean pulse rate for all people is 72 bpm with a variance of 16. What is the probability that the sample mean is less than 70 bpm

1. according to the internal revenue service, the mean tax refund for the year 2007 was $2,708. assume the standard deviation is $650 and that the amounts refunded follow a normal probability distribution. a. what percent of the refunds are more than $3,000? b. what percent of the refunds are more than $3,000 but less than $4,000? c. what percent of the refunds are less than $2,000?