Question

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?

Answer 1

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.