Question

Erica can paint her room 5 hours .If she had her friend Rachel help her , they can paint the room together in 3 hours .How long would it take for Rachel to paint the room alone , if Erica wanted to go play tennis for the afternoon ?

Answer 1

7 hours 30min

Explanation:

Step one :

Given data

We are told that Erica can paint 1 room in 5hours

Her work rate is 1/5 room per hour

And also with the assistance of her friend they can paint 1 room in 3 hours

Hence their combined work rate is 1/3 room per hour

Step two

The combined work expression is

1/A+1/B=1/T

Where A=Erica's work rate

B=Rachael's work rate

T=combined work

1/5+1/B=1/3

1/B=1/3-1/5

1/B=5-3/15

1/B=2/15

B=15/2

B=7.5 hours

It will take Rachel 7 hours 30min to paint the room