Help with practice quiz-math question.?

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rain.creation

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I want to know how to solve this. It's been a while since I was in algebra and I dont even know where to begin. If it's something simple and stupid then I'm sorry. But I really want to know.

Please tell me HOW to solve this, I'm not looking for the answer. I just want to know how.

2. If Sally can paint a house in 4 hours, and John can paint the same house in 6 hour, how long will it take for both of them to paint the house together?

A. 2 hours and 24 minutes
B. 3 hours and 12 minutes
C. 3 hours and 44 minutes
D. 4 hours and 10 minutes
E. 4 hours and 33 minutes
 
Sally paints 1/4 of the house in an hour and John paints 1/6 of the house in an hour. 1/4+1/6 = 3/12+2/12 = 5/12 so working together they paint 5/12 of the house in an hour. So it takes them 12/5 hours to paint it. 12/5=2 & 2/5 and since 2/5 hour is 24 minutes the answer you want is A.

Of course, in practice, it will be slower with two people because they'll stop and have a chat.

I hope this helps.
 
In 1 hour Sally can paint 1/4 of the house;
In 1 hour John can paint 1/6 of the house;
In 1 hour they together can paint 1/4 + 1/6 = 5/12 of the house.

1 hour = 60 minutes

60 : 5/12 = x : 1
x = 60 : 5/12 = 60*12/5 = 144 minutes = 2 hours and 24 minutes.

A. 2 hours and 24 minutes

Bye
gilvi
 
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