Expert: Bobby Soltani - 1/4/2005

Question
Hi its me jermaine again, I still dont under stand the one problem i had and i could really use your help if you could please help me just solve the probelm out step by step and the answer.

1. 12a - 5b = 18
  15a -  5b =30

Answer
Hi Jermaine,

We want to manipulate one of the equations so that one of the variables will drop out when we add the two equations together.  Since we have -5b in both equations we can just subtract the two and the -5b will drop out.  Let's do that.

1. 12a - 5b = 18
2. 15a - 5b = 30

subtract the second equation from the first

-3a + 0b = -12
-3a = -12
divide both sides by -3
a = 4
plug a=4 back into the first equation
12*4 - 5b = 18
48 - 5b = 18
subtract 48 from both sides
-5b = -30
divide both sides by -5
b = 6

That's it.  Let me know if you have questions.

Bobby