Tom can clean the store in twelve hours. If Sandy helps, it takes them ten hours. Without help, how long would it take Sandy to do the same thing?

1 Answer
Apr 2, 2016

It will take 60 hours for Sandy to do the same.

Explanation:

Tom can clean the store in 12 hours, so in one hour Tom cleans 1/12 of the store.

Tom and Sandy together clean the store in 10 hours,

so in one hour they clean 1/10 of the store.

Hence in one hour Sandy cleans 1/10-1/12 of the store.

or (6xx1)/(6xx10)-(5xx1)/(5xx12)=6/60-5/60=1/60 of the store.

As Sandy cleans 1/60 of the store in one hour,

It will take 60 hours for Sandy to do the same.