Name: Joe

Who is asking: Student
Level: Secondary

Question:
whats the answer to this question?

3x+y=11
x+2y=-3

its substitution method i am having alot of trouble figuring it out. send the answer as soon as possible. thank you



Hi Joe,

I see two reasonable choices here.

  1. Solve the first equation for y and substitute into the second equation.

  2. Solve the second equation for x and substitute into the first equation.
There are two other choices, solve the first equation for x and substitute into the second or solve the second equation for y and substitute into the first. Both of these choices lead immediately to fractions so I would chose one of ther first two. I don't think either is easier than the other so I am going to select the first choice.

Solve the first equation for y.

3x + y = 11

thus

3x + y -3x = 11 - 3x

or

y = 11 - 3x

Substitute into the second equation.

x + 2y = -3

thus

x + 2(11 - 3x) = -3

x + 22 - 6x = -3

-5x = -25

Thus

x = 5

Finally substitute x = 5 into either of the equations you started with to find y.

Now try it the other way. Solve the second equation for x and substitute into the first equation. You should find the same answer.

Cheers,
Penny
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