please help me. . . stupid 5th grade math...?

Question

Solve using substitution?? i was sick this week and dont understand!

x+2y=5
x+y=2
_________
x+3y=12
2x-4y=4
________
3x+y=1
x=2y+5

thank you!

Answer 1

holy cow!!! That is pretty advanced math for 5th grade....I didnt do that stuff until i was in 9th grade. Anyway it's been a long time since I have done that kind of math...I regret to say I can't help you with that.

Answer 2

Hmm.. I actually forgotten what it means by using subtitution but here's how I'm doing it. Maybe it is substitution after all, just can't remember all these 'formal method', you know? :)

Ok here I go

First question: x+2y = 5 and x+y = 2
Notice that there are 2 variables, why don't we cut down one of the variable so that it will be easier to calculate. From the equations, we see that it is much easier to get rid of x as we can do that by substracting one equation with the other.

x + 2y = 5
x + y = 2
------------- (-)
y = 3

see that the x - x = 0, so that left with 2y - y = y and 5-2 = 3, and so y = 3 and by substituting the known value of y of 3 back to either equation, it will give you x = -1

See, easy right. Now try this method with the other 2 questions. However for question 2, you need to do some adjustment by multiplying the top equation by 2 so that it will give you 2x + 6y = 24. This way it will easier to get rid of the common factor, the 2x. That left you with 6y - (-4y) = 10y and 24-4 = 20. From this you know that 10 y = 20 and y therefore is 2.

As for question 3, you just have to move 2y to the other side so that it looks like x-2y = 5. The rest of the step you just follow question 2 above.

Answer for question 2, x = 6 and y = 2
Answer for question 3, x = 1 and y = -2

Good luck!

Answer 3

solve for one variable, then use it in the other equation.

1) It is easiest to start with the second equation because it is more simple. Subtract the y to the other side, leaving you with x=2-y
Then use (2-y) anywhere there is an x in the first equation.
Substituting in, you get 2-y +2y=5
Next combine your Ys. 2y-y=1y
Now you have 2+y=5
Subtract 2 from both sides
Leaving you with y=5.
Good, now you have y. Now just sub into either equation 5 wherever there is a y.
Easiest is the second equation: x+5=2
Subtract 5 from both sides and you get x=-3

So, y=5 and x=3

I won't work out the others. email me at [e-mail] with your answers to the other problems or any other questions you may have. I'll tell you if you're right or wrong and how to fix it.

Just use the same steps:
1) get one variable by itself
2) replace that variable in the other equation
3) solve for the remaining variable
4) use your solution in either equation to solve for the other

Good luck

Answer 4

x+2y=5
x+y=2
_________
from the first one x = 5-2y
substitute into second
x+y=5-2y+y=5-y=2
from here y =5-2 = 3
then x = 5-2y = 5 - 2*3 = -1
so the solution is (-1,3)


x+3y=12
2x-4y=4
________
from the first one x = 12 - 3y
substitute that into second one
2x - 4y = 2(12-3y)-4y = 24-10y = 4
from there 10y = 20 and y =2
now x = 12 - 3y = 12 - 3*2 = 6
so, the solution is (6,2)


3x+y=1
x=2y+5
substitute 2y + 5 for x in the first equation
3(2y+5)+y = 1
6y + 15 + y - 1=0
7y=-14
y=-2
now x = 2y + 5 = -4 + 5 = 1

the solution is (1,-2)

Answer 5

i am assuming that they are of diff questions
1. x+2y =5
x+y = 2 ==> x= 2-y

sub the 2nd equation back into the 1st
(2-y)+2y = 5
2+y = 5
y = 3
x= 2-3 = -1

2.
x+3y = 12 ==> x = 12-3y
2x-4y =4
sub x= 12-3y into the 2nd eqn
2(12-3y) -4y = 4
24-6y-4y =4
24-10y = 4
20 =10y
y = 2
x = 12-3(2)
x =6

3.
3x +y =1
x= 2y + 5

sub the 2nd eqn into the 1st

3(2y +5) +y = 1
6y + 15+y =1
7y = -14
y = -2
x = 2(-2) +5
x =1

Answer 6

consider the first one:

(1) x+2y=5
(2) x+y=2 : make the equation = y

so, (2) becomes y=2-x

sub (2) into (1)
x+2(2-x)=5
x+4-2x=5
4-x=5 (minus 4 from both sides)
-x=1
therefore x= -1

to find y:
sub x= -1 into (1)
-1+2y=5 (add 1 to both sides)
2y=6 (divide both sides by 2)
y=3

therefore:
x= -1
y=3

Answer 7

what you do in situations like these is use ONE of the equations in your set and solve for a variable, then substitute what you got for that variable into the other one. this second step will let you get 1 variable in an equation. You can solve for that variable, then put that answer back into the first equation to solve for the first one.

example: in your first set:

x+y=2 so if you solve for x you get x=2-y
then put it into the other equation instead of x
(2-y)+2y=5 and solve for y
-y+2y=3
y=3
then put that back into the first equation and solve for x
x+3=2
x=-1
you can check your first equation by using this value of x and your value of y
-1+6=5

there you go hope i helped

Answer 8

x+2y=5
x+y=2

Rewrite either to solve for X:

x=2-y

substitute that for X in the other equation
(2-y) +2y = 5

2+y=5
y = 3

go back to the one you solved for x:

x=2-y = 2-3 = -1

X = -1

There's the method...

the rest are easy.

Answer 9

first one would be X= 2-y for the bottom then just stick that into the top whereever u see an x. so it would be 2-y +2y=5

Answer 10

1)x= -1 & y=3
2)x=6 & y=2
3)x=1 & y=-2

Answer 11

Multiply the 2nd eq by -2

-2x - 2y = -4

Add 1st eq onto the new 2nd eq

-x = 1

x = -1

Plug in to solve for y

-1 + 2y = 5

2y = 6

y = 3

x = -1, y = 3
---------------------------------
Multiply 1st eq by -2

-2x - 6y = -24

Add with 2nd eq

-10y = -20

y = 2

Plug in to solve for x

x + 6 = 12

x = 6

x = 6, y = 12


Now using the same method i think you can do the last one