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.
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Regards,
Chitra
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