1. 3x+y=5

2x-y=10

2. 2x+2y=3

X-4y=-1

1. X=5 and Y=-15

2. X=1 and Y=0.5

1. Since y in first equation is positive and y in second equation is negative, the easiest was to solve this system is:

3x+y+2x-y=5+10

5x=15

x=3

Now use the x to find y:

3*3+y=5

9+y=5

y=5-9

y=-4

2. You can either multiply the first equation by 2 so that we get the same numbers in front of the y but with different signs or simply express one of the variables and write it in second one.

First way:

2x+2y=3 / *2 (multyplying by 2)

4x+4y=6 (that's our first equation)

x-4y=-1 (that's our second equation)

now we just add the equations:

4x+4y+x-4y=6 + (-1)

5x=6-1

5x=5

x=1

now we find y:

1-4y=-1

-4y=-1-1

y=-2/-4

y=1/2

Second way:

We express x from the second equation and get:

x=-1+4y

now we change x in the first equation with our new x:

2 * (-1+4y) + 2y=3

-2+8y+2y=3

10y=5

y=1/2

x=-1+4 * (1/2)

x=-1+2

x=1