PreCalculus Questions

Question

It takes Willy 10 hours to sort through a set of documents. Lilly can do it in 5 hours. If they worked together, how many hours would it take them?

Answer 1

It's usually helpful to think in terms of work per unit time, rather than time required to complete the entire job.

 

Willy can do 1/10 of the job in one hour.

 

Lilly can do 1/5 of the job in one hour.

 

So, working together, they can complete 3/10 of the job in one hour.

 

Take the reciprocal of 3/10.  They can complete the entire job in 10/3 = 3 1/3 hours.

 

Expressed mathematically, 1/10 + 1/5 = 1/x.