Systems of linear equations

[Melaniew]

The directions say to use substitution or elimination by addition.

x+y=1
0.3x-0.4y=0

My problem is at the back of the book the answer is in fractions. I started off by trying to eliminate the y's by getting whole numbers. I have no idea how to start solving this problem. Any help would be apprciated.

 

[arthur ohlsten]

eq1) x+y=1
eq2) .3x-.4y=0

by substitution
eq1)
x=1-y substitute into eq2
.3[1-y] - .4y = 0
.3 -.3y -.4y=0
.3-.7y=0
.3=.7y
y=3/7 answer

substitute for y in either eq1 or eq2. I will use eq1, I think its easier.
x+3/7=1
x=1-3/7
x=4/7 answer
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SECOND METHOD
eq1 x+y=1
eq2 .3x-.4y=0

multiply equation 1 by .4 to make y terms exact
eq1) .4x+.4y=.4
eq2) .3x-.4y=0
add the equations
.7x=.4
x=4/7 answer

you multiply eq1 by [-.3] so x terms have same values but negative. then add the equations.

Arthur