Marcy can do a job alone in 5 hrs. If Mark helps her, they can do the job together in 3 hours. How long would Mark take working alone?

Question

Solve this assuming no denominator is zero

Answer 1

T₁ = time it takes Marcy to do job alone = 5 hours

 

T₂ = time it takes Mark to do job alone = ?

 

T = time it takes for them to do job working together = 3 hours

 

1/T = 1/T₁ + 1/T₂

 

1/T₂ = 1/T - 1/T₁ = 1/3 - 1/5 ⇒ T₂ = 7.5 hours

 

It takes Mark 7.5 hours to do the job working alone.