Originally Posted by

**mpoderoso** this problem is hurting me. It's from the National University of Colombia 2007 entrance exam (translated from Spanish), and I need to understand it's principles for their test in two days.

When one adds a hard drive to a new personal computer, the new system costs $2900 x 10^3. One knows that 1/3 of the computer, plus 1/5 of the hard drive adds up to $870 x 10^3. If x represents the value of the computer and y the hard drive, a system of linear equations that permits calculating the value of the hard drive is:

A.

x - y = 290 x 10^4

5x + 3y = 1305 x 10^4

B.

x+y=290 x 10^4

3x + 5y = 87 x 10^4

C.

x - y = 290 x 10^4

5x + 3y = 87 x 10^4

D.

x + y = 290 x 10^4

5x + 3y = 1305 x 10^4

The answer is D, but I'm not sure why. Please explain it if you can. Thank you