introductory algebra

I had these problems on my test and for some reason got them wrong. Here are the problems:

Solve:
x-y=9
x+y=1

The test states that the answer is (5,-4)

I've checked ,y work and used substitution to solve this and still get x=4, y=-5.

The second problem is:
Solve the system of equations by graphing.
a=1/2b+5
a-4b=-2

Again i got the reverse of this; (2,6).

I have been at these for several hours and want to pull my hair out. Are my answers really wrong or is it the test? HELP!

Thanks

1. 👍
2. 👎
3. 👁
1. x-y=9
x+y=1

The test states that the answer is (5,-4)

I've checked ,y work and used substitution to solve this and still get x=4, y=-5.
------------------------
4 - -5 = 9 yes
4 + -5 = -1, not +1 wrong
2 x = 10
x = 5
then
5+y = 1
y = -4

1. 👍
2. 👎
2. a=1/2b+5
a-4b=-2

substitute (1/2) b + 5 for a

(1/2) b + 5 - 4 b = -2

b + 10 - 8b = -4

-7 b = -14
b = 2
then
a = 1 + 5 = 6

1. 👍
2. 👎

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