Answer:
About 13 hard drives
Step-by-step explanation:
Using the rule of three, if studying the access speed of 40 hard drives gives the maximum estimate error of 15, then we multiply 5 (which is the number of estimates that are sought in a second attempt) by 40 hard drives divided by 15 as maximum estimate number. We get a total of 13.33, therefore we would need an approximate of 13 hard drives to reduce the maximum estimation error to 5.
40 hard drives ---- 15
13.33 hard drives ---- 5
(40 * 5) / 15 = 13.33 hard drives