SAT Math Q: If ax+4=2y+8, bx+2=4y-11, & a=3-b, then which is true?

[kac2205]

ax+4=2y+8
bx+2=4y-11


In the equations above, a and b are constants. If a is 3 minus b, which of the following is true?


A) x is y minus 9
B) x is y minus 3
C) x is twice y minus 9
D) x is twice y minus 3

I have the answer (D), I just have no clue how to solve this. I've tried substitution and elimination but there are so many variables. Do I try just putting numbers in for a and b? I've tried every which way to solve this, but the right way it seems.

 

[tkhunny]

The methods you suggested should work just fine. Please demonstrate your efforts.

You are given a = 3 - b. Why not substitute that and cut down on the number of variables.

If you don't like the remaining 'b', solve each equation for b and see where that leads you.

 

[stapel]

ax+4=2y+8
bx+2=4y-11

In the equations above, a and b are constants. If a is 3 minus b, which of the following is true?

A) x is y minus 9
B) x is y minus 3
C) x is twice y minus 9
D) x is twice y minus 3

I have the answer (D), I just have no clue how to solve this. I've tried substitution and elimination but there are so many variables. Do I try just putting numbers in for a and b? I've tried every which way to solve this, but the right way it seems.

Please reply with a clear listing of your steps and reasoning for at least one of your "every which way" solutions, so we can see what's going on. Also, if you tried plugging in the given answer-options, where did this lead?

Please be complete. Thank you!