Posted by tyler on Friday, February 22, 2013 at 12:50pm.
The sum of twice a number and another number is 24. The difference of twice the first number and the other number is 12. Which system would model this situation, and what is the solution?

Math  JJ, Friday, February 22, 2013 at 12:53pm
x = 1st number and y = second number
2x + y = 24
2x  y = 12
Can you finish from here? Add the two equations to eliminate y and solve for x.
Then find y.
Be sure to check both x and y in both equations to be sure you are correct. 
Math  Damon, Friday, February 22, 2013 at 1:00pm
2 x + y = 24
y  2x = 12
4 x = 12
x = 3
y = 24  6 = 18
check
6 + 18 = 24 yes
18  6 = 12 yes
note you could have written
2 x + y = 24
2 x  y = 12
2 y = 12
y = 6
2x + 6 = 24
x = 9