SOLUTION: Question #21 is Use the substitution method to solve the linear system. These are the equations:2x+3y=31, y=x+7 i tried to substituted it then it looked like this 2x+3(x+7)=31 th

Question 64389This question is from textbook McDougal Littell
: Question #21 is Use the substitution method to solve the linear system. These are the equations:2x+3y=31, y=x+7 i tried to substituted it then it looked like this 2x+3(x+7)=31 then i combined like terms and it looked like this 5x+7=31 i took away the 7 to both sides and got 5x=24 i divided both sides by 5 to isolate the variable and got x=4.8 then i plugged that in for the next equation and i got 2(4.8)+3y=31 i solved the x so i got 9.6+3y=31 i subtacted the 9.6 and then it looked like this 3y=21.4 i dived it by three and i ended up with y=7.13 so the answer i got was (4.8,7.13) but the answer in the back of the book says it's (2,9) i don't know what i did wrong. please help me?
This question is from textbook McDougal Littell

Found 2 solutions by stanbon, chitra:
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
Question #21 is Use the substitution method to solve the linear system. These are the equations:2x+3y=31, y=x+7 i tried to substituted it then it looked like this 2x+3(x+7)=31 then i combined like terms and it looked like this 5x+7=31
Whoops: Right here you should have 5x+21=31.
Then x=2
Cheers,
Stan H.

Answer by chitra(359) (Show Source): You can put this solution on YOUR website!
This is quite a simple problem..

Here goes the solution.

The given set of equations are:

2x + 3y = 31 ---------->(1)

y = x + 7 ---------->(2)

Substituting (2) in (1), we get:

2x + 3(x + 7) = 31

2x + 3x + 21 = 31 -------------> (3)

[you have not multiplied the 3 with 7. So one term is missing from the expression]

Hence, (3) can be written as:

5x + 21 = 31

Subtract 21 from both the sides.

5x = 31 - 21

5x = 10

Therefore x = 2

Now substitute the value of x in either of the equations.

y = x + 7

y = 2 + 7

So we get:

y = 9

Hence, the co-ordinates are (2, 9)

Thus, the solution.

---
Regards,
Chitra

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