P can wash the windows of house in 10 hours.His friend can wash same windows in 8 .How long together take them?

Question

It's a rate question.

Answer 1

In one hour the first person washes 10% (1/10) of the windows whereas the second person washes 12.5% (1/8) of the windows. So together in a single hour they can wash 22.5% of the house. We want to find how long it will take for them to wash 100% of the house. So the total amount of hours it would take is 100/22.5=4.44 hours.

Answer 2

So, Holly, in one hour, P can wash 1/10 of the windows and his friend can wash 1/8.

 

If we let t = the time, then (1/10)t + (1/8)t = 1 (house)

 

The LCM of 10 and 8 is 40.

 

(4/40)t + (5/40)t = 1

 

(9/40)t = 1

 

t = 40/9 = 4 4/9 hours = 4 hours, 27 minutes.

 

Hope this helps!