Algebra word problem

Question

there are 630 dishes that need to be rinsed. Juan can rinse them in 70 minutes by himself. it will take his friend Sam 105 minutes to rinse these dishes. how long will it take them if the rents these 630 dishes together

Answer 1

t = minutes the two work together

 

In one minute Juan can clean 630/70, or 9 dishes.

In one minute Sam can clean 630/105, 6 dishes.

 

9t + 6t = 630

15t = 630

t = 42

 

Working together they can clean the dishes in 42 minutes.