Question

A combination lock for a bicycle has four dials, each with the numbers from 1 to 6. If you have forgotten the combination that opens the lock, how long will it take you to try all the combinations, at a rate of one every 5 seconds

Answer 1

1.8 hours

Explanation:

The number of combinations is 6^4 = 1296. At one every 5 seconds, it will take 5·1296 = 6480 seconds to try them all. There are 3600 seconds in an hour, so that is ...

(6480 s)/(3600 s/h) = 1.8 h

It will take 1 hour and 48 minutes to try them all.