anujtsingh wrote:

In assembling a Bluetooth device, a factory uses one of two kinds of modules. One module costs $6.25 and the other one, that is cheaper, costs $2.50. The factory holds a $70 worth stock of 22 modules. How many of the modules in the stock are of the cheaper kind?

(A) 4

(B) 8

(C) 12

(D) 16

(E) 18

We can also solve the question using ONE VARIABLE.

Let x = the number of cheap modules

So, 22 - x = the number of expensive modules

So, the VALUE of the cheap modules = 2.5x

So, the VALUE of the cheap expensive = 6.25(22 - x)

The TOTAL value = 70 dollars, so we can write: 2.5x + 6.25(22 - x) = 70

Expand to get: 2.5x + 137.5 - 6.25x = 70

Simplify: -3.75x + 137.5 = 70

Rearrange to get: -3.75x = -67.5

Solve: x = 18

Answer: E

Aside: Here's a free video on deciding how many variables to assign on questions like this:

http://www.gmatprepnow.com/module/gmat- ... /video/906 Cheers,

Brent

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