The Student Room Group

Simultaneous equations

Scroll to see replies

Reply 20
Original post by RDKGames
12x + 8y = 88 ... (1)
10x + 8y = 46 ... (2)

Subtract (2) from (1) on both sides.

(1)(2):(12x+8y)(10+8y)=(88)(46)(1)-(2): (12x+8y)-(10+8y)=(88)-(46)

and you can solve that.


would it be x = 21??
Original post by Jack_Tomlin
would it be x = 21??


Yep. Now substitute that back into one of the two equations and you can find what y is.
Reply 22
Original post by RDKGames
Yep. Now substitute that back into one of the two equations and you can find what y is.


Ok so like this?

126 + 2y = 22
105 + 4y = 23
Original post by Jack_Tomlin
Ok so like this?

126 + 2y = 22
105 + 4y = 23


No.

You found that x=21. Now choose whichever equation you want to substitute it into, it doesn't matter, you would get the same answer from either.

Let's choose the second one for instance: 10x+8y=4610x+8y=46
Since we know x=21 we can replace x with 21

10(21)+8y=4610(21)+8y=46

and you can solve from there.
Reply 24
Original post by RDKGames
No.

You found that x=21. Now choose whichever equation you want to substitute it into, it doesn't matter, you would get the same answer from either.

Let's choose the second one for instance: 10x+8y=4610x+8y=46
Since we know x=21 we can replace x with 21

10(21)+8y=4610(21)+8y=46

and you can solve from there.


So we always sub into the equations where we made the coefficients the same not the first lot we are given?
Original post by Jack_Tomlin
So we always sub into the equations where we made the coefficients the same not the first lot we are given?


You can sub into either, the ones you make up are only multiples of the original ones, they don't affect the final answer after you simplify everything.
Reply 26
Original post by RDKGames
I feel the same way lol, but would't want to be rude or anything. I wonder what year OP is in.


No idea but I expect 7 or 8 as these are extremely basic simult eqns. Don't know why this thread has so many posts lol

Posted from TSR Mobile
Original post by Jack_Tomlin
So we always sub into the equations where we made the coefficients the same not the first lot we are given?


It doesn't matter as long as you replace one variable so you only get one variable left in the equation. When you made the coefficients the same, you only multiplied both sides by a scale factor so the equations are basically still the same.
Reply 28
Original post by 98matt
this thread is infuriating. Add them together, it's not hard. Watch some tutorial video if you're unsure. x=2 y = -0.5 is the solution

Posted from TSR Mobile


Sorry but I'm sitting the new GCSE maths exam next year foundation tier and a alot of the higher tier topics are moving to foundation as well.
Original post by Jack_Tomlin
Sorry but I'm sitting the new GCSE maths exam next year foundation tier and a alot of the higher tier topics are moving to foundation as well.


I don't mean to sound rude but it's clear that you're not sure what you're doing at all. I would go on YouTube and watch a few videos on simultaneous equations and watch how other people solve the questions and then try some yourself from a textbook.
Original post by NeverLucky
I don't mean to sound rude but it's clear that you're not sure what you're doing at all. I would go on YouTube and watch a few videos on simultaneous equations and watch how other people solve the questions and then try some yourself from a textbook.


Agreed. He just seems as if he was thrown some simultaneous equations without any background knowledge on them. :/

Original post by Jack_Tomlin
Sorry but I'm sitting the new GCSE maths exam next year foundation tier and a alot of the higher tier topics are moving to foundation as well.


OP, you can watch these videos made by my teacher and I'm sure they will prove extremely helpful. https://www.youtube.com/watch?v=_hsUrfF9rOs

https://www.youtube.com/playlist?list=PL0sgfvQGLNJujLLbZQPPdCKXNkRM7X_9c
(edited 7 years ago)

Quick Reply

Latest