Posted by **Courtney** on Saturday, November 10, 2007 at 4:02pm.

I need help figuring out these two problems. I think I have the right idea about solving them but I'm not exactly sure.

8. Two companies market new batteries targeted at owners of personal music players. DuraTunes claimes a mean battery life of 11 hours, while RockReady advertises 12 hours.

-Suppose the standard deviations are 2hours for DuraTunes and 1.5 hours for RockReady. You are headed for 8 hours at the beach. Which battery is most likely to last all day? Explain.

10. John Beale of Stanford< CA, recorded the speeds of cars driving past his house, where the speed limit read 20 mph. The mean of 100 readings was 23.84 mph, with a standard deviation of 3.56 mph. (He actually recorded every car for a 2-month period. These are 100 representative readings.)

- How many standard deviations from the mean would a car going under the speed limit be?

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