20. The life of a particular battery is known to follow a normal distribution , with a mean of 2026 hours and a standard deviation of 99 hours. a. What percent of batteries last less than 2221 hours? ( Round to 4 decimal places) b. The 85 th percentile is represented by what number of hours of battery life? c. What is the probability that a randomly selected battery will last more than 2150 hours?

21. The systolic blood pressure of adults in the USA is nearly normally distributed with a mean of 118 millimeters of mercury (mmHg) and standard deviation of 17.

Someone qualifies as having Stage 2 high blood pressure if their systolic blood pressure is 160 or higher.Stage 1 high BP is specified as systolic BP between 140 and 160.

Give your answers rounded to 4 decimal places. a. What is the probability that an adult in the USA has stage 2 high blood pressure? b. What is the probability that an adult in the USA has stage 1 high blood pressure? c. Your doctor tells you you are in the 30th percentile for blood pressure among US adults. What is your systolic BP? _____ mmHg

d. What is the systolic blood pressure that cuts off the top 2.5% of adults in the USA? ______ mmHg

22. The number of chocolate chips in a popular brand of cookie is normally distributed with a mean of 24 chocolate chips per cookie and a standard deviation of 2.3 chips. When the cookies come out of the oven, only the middle 90% in terms of the number of chocolate chips are acceptable (the rest are considered defective). What are the cutoff numbers for the number of chocolate chips in acceptable cookies? (Give your answers to three decimal places) _______ and ________