# Statistics & Probability

posted by
**Alia**
.

A researcher conducted a study of the access speed of 45 hard drives and concluded that his maximum error of estimate was 28. If he were to conduct a second study to reduce the maximum error of estimate to 7, about how many hard drives should he include in his new sample?

Select one:

a. 720

b. 45

c. 90

d. 180

Please can someone explain me how to do the above problem.

Thanks!