SAT math help

<p>Got this from a kaplan sat practice test I took.</p>

<p>Ambrose, working alone, can paint a certain room in 8 hours. Either one of Benedict or Charles, working alone, can paint the room in 4 hours. If all three people, working at these rates, work together to paint the room, what fraction of the room is painted by Ambrose?</p>

<p>Ive seen a few problems like these but I dont think Ive ever gotten one correct. So how would I approach a question like this? Is there some kind of formula? How do i solve this?!</p>

<p>Btw this was a student produced q, and I dont have the answer. Kaplan suks...., on my answer sheet they only marked if the answer was right or wrong.</p>

<p>Work Rate x Time = Job Done
Ambrose Rate x 8 = 1
AR = 1/8
BR = 1/4
CR = 1/4</p>

<p>t = time
1/8t + 1/4t + 1/4t = 1
t + 2t + 2t = 8
5t = 8
t = 8/5</p>

<p>1/8(8/5) = 1/5 = Ambrose's fraction </p>

<p>*Somebody check if this is correct.</p>

<p>I dont really understand how you got from
1/8t + 1/4t + 1/4t = 1 to t + 2t + 2t = 8
can you clarify that please</p>

<p>multiplied both sides by 8</p>

<p>Just think about it this way:
Say Ambrose does X work. Each of the other two can do 2X work, and together 4X work. All three of them therefore do 5X work, and Amborse is X worth of this work. So x/5x=1/5</p>