Hi, can someone pls give me an idea how to do this? Thanks!

Use substitution to solve the following system.

L+r+s=20
R=l+3
L+5r+10s=129

I have to solve for all the variables, and am really confused. Any help is greatly appreciated.

1 answer

I would be confused too, if I had 5 variables but only 3 equations
Unless R =r and L = l

so rewriting it:
l+r+s=20
r=l+3
l+5r+10s=129

sub r = l+3 into the first:
l + l+3 + s = 20 ----> 2l + s = 17 **
sub r = l+3 into the last:
l + 5(l+3) + s = 129
6l + s = 114 ***

subtract ** from ***
4l = 97
l = 97/4
into r = l+3 = 97/4 + 3 = 109/4

into l+r+s=20
97/4 + 109/4 + s = 20
s = -63/2
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