SOLUTION: if a:b = 4:5 and a:(b+c)= 3:7 then a:c is a) 1:2 b) 2:5 c) 4:7 d) 12:13 e) 20:21

Algebra ->  Percentage-and-ratio-word-problems -> SOLUTION: if a:b = 4:5 and a:(b+c)= 3:7 then a:c is a) 1:2 b) 2:5 c) 4:7 d) 12:13 e) 20:21       Log On


   

Question 237580: if a:b = 4:5 and a:(b+c)= 3:7 then a:c is
a) 1:2 b) 2:5 c) 4:7 d) 12:13 e) 20:21

Answer by nyc_function(2741) About Me  (Show Source):
You can put this solution on YOUR website!
Let a = 4
Let b = 5
Then we can make:
4/(5 + c) = 3/7
Cross-multiply:
3(5 + c) = 4(7)
15 + 3c = 28
3c = 28 - 15
3c = 13
c = 13/3
We are looking for a:c, which is really a/c.
We know a and we just found b.
So, plug and chug.
4/(13/3) = 12/13 = 12:13
Answer is choice d.
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By the way, a:b can also be written a to c, which can also be written as a/c.
They all mean the same thing.
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Think about it this way:
Batman:Robin = Batman to Robin = Batman/Robin