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 Post subject: GMAT FunctionsPosted: Tue Sep 07, 2010 3:49 am

Joined: Sun May 30, 2010 3:15 am
Posts: 424
Suppose the number of fans at a baseball game is given by the function b(x) = 150x – 6 and the number of fans at football game is given by f(b) = 2b + 12. What is the value of x when there are 1200 fans at the football game?
A. 2
B. 5
C. 4
D. 3
E. 7

(C) The first thing to do is to substitute f = 1200 into the second equation to solve for b:
b = (f – 12)/2 = (1200 – 12)/2 = 1188/2 = 594.

Now, we substitute b = 594 into the first equation to solve for x:
x = (b + 6)/150 = (594 + 6)/150 = 4.

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I'm totally stuck on how you get to b = (f – 12)/2, can you elaborate a little more? Thanks.

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 Post subject: Re: math (test 2, question 18): algebraPosted: Tue Sep 07, 2010 4:01 am

Joined: Sun May 30, 2010 2:23 am
Posts: 498
When we substitute f = 1200 into the second formula:

f(b) = 2b + 12

we get equation:

1200 = 2b + 12

and solve it for b:

b = (1200 – 12)/2
b = 594
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We could also solve for b first and then plug in f = 1200. (As it is done in question explanation). NOTE that for simplicity we use denotation f instead of f(b).

f(b) = 2b + 12
f = 2b + 12
f – 12 = 2b
b = (f – 12)/2

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