Benny wants to estimate the mean lifetime of energizer batteries, with a confidence level of 97%, and with a margin of error not exceeding ±10 hours. if the standard deviation of the lifetime is known to be 55 hours, how many batteries does benny need to sample?

143 batteries does Benny need to sample

Explanation:

Given data

confidence level = 97%

error  = ±10 hours

standard deviation SD = 55 hours

to find out

how many batteries does Benny need to sample

solution

confidence level is 97%

so a will be 1 - 0.97 = 0.03

the value of Z will be for a 0.03 is 2.17 from standard table

so now we calculate no of sample i.e

no of sample  = (Z× SD/ error)²

no of sample = (2.16 × 55 / 10)²

no of sample = 142.44

so  143 batteries does Benny need to sample

explanation:

as the height from which the ruler was dropped increased, the speed of the ruler at ryan's hand increased.

hi there!

out of the two, (b) precision would be more reasonable.   however, both a and b could be pretty reasonable.

-awesomerepublic   : )