Posted by Kristin on Saturday, March 13, 2010 at 1:03am.
Can someone help me solve the following problems using the substituion method? I need to find the ordered pairs and I do not get it.... Here they are
1)
6m+n=47
m4n=12
2)
6x+4y=10
7x+y=57
3)
5x+7y=43
4x+y=25

Math  Reiny, Saturday, March 13, 2010 at 8:06am
I use substitution when I notice that in one of the equations one of the variables has a coefficient of 1
Then solve for that single variable
e.g. in #2
7x + y = 57 ,
y = 7x + 57
now sub that into the other equation
6x + 4y = 10
6x + 4(7x+57) = 10
6x + 28x + 225 = 10
34x =  218
x = 218/34 =  109/17
then y = 7(109/17) + 57
y = 206/17
do the other two the same way

Math  Kristin, Saturday, March 13, 2010 at 9:52am
Okay but the homework is saying the answer is (7,8) so how would they have gotten that from the equation you did above?

Math  Reiny, Saturday, March 13, 2010 at 12:04pm
I made a transcript error.
After 6x + 4(7x+57) = 10 it should have been
6x + 28x + 228 = 10
I had 2 errors in copying that line, sorry about that
Now i works out

Math  Kristin, Saturday, March 13, 2010 at 5:11pm
Okay so what about number one it is a + and the a  for the second problem how do you figure a subtitution problem like that? do the signs make a difference?

Math  Kristin, Saturday, March 13, 2010 at 5:16pm
For number 3 I got (6.7,51.8) is this correct?
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