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# How to make y the subject of these formulae? Tweet

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1. How to make y the subject of these formulae?
I've totally forgotten how to make y the subject.

How would I make y the subject of 2b=3(y+8)
2. (2/3)b-8=y divide both sides by 3 then minus 8.

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3. Re: How to make y the subject of these formulae?
(Original post by mrppaulo)
(2/3)b-8=y divide both sides by 3 then minus 8.

This was posted from The Student Room's iPhone/iPad App
Could you explain why you did that?
4. Re: How to make y the subject of these formulae?
(Original post by multiplexing-gamer)
Could you explain why you did that?
Because you said you wanted to make y the subject.
5. Re: How to make y the subject of these formulae?
(Original post by FXX)
Because you said you wanted to make y the subject.
Sorry, what I meant was could you explain each step?
6. Re: How to make y the subject of these formulae?
(Original post by multiplexing-gamer)
Sorry, what I meant was could you explain each step?
If he didn't he would have 3y, you only wanted y.
7. Re: How to make y the subject of these formulae?
(Original post by multiplexing-gamer)
Sorry, what I meant was could you explain each step?
2b=3(y+8)

You want to get y out of the brackets, so move the 3 over to the left hand side. You do this by dividing each side by 3.

(2/3)b=y+8

Then you want y on its own, which you can do by subtracting 8 from each side.

(2/3)b-8=y
8. Re: How to make y the subject of these formulae?
(Original post by FXX)
2b=3(y+8)

You want to get y out of the brackets, so move the 3 over to the left hand side. You do this by dividing each side by 3.

(2/3)b=y+8

Then you want y on its own, which you can do by subtracting 8 from each side.

(2/3)b-8=y
Thanks I understand now!
9. Re: How to make y the subject of these formulae?
How would make y the subjectmof
t(5-y) = 2ry

Would the first step be divide t(5-y) by y?
10. Re: How to make y the subject of these formulae?
(Original post by multiplexing-gamer)
How would make y the subjectmof
t(5-y) = 2ry

Would the first step be divide t(5-y) by y?
no

the first step(s) involve gathering all of the y together

I will do a similar example
11. Re: How to make y the subject of these formulae?
(Original post by TenOfThem)
no

the first step(s) involve gathering all of the y together

I will do a similar example
Ok thanks for the example. But both sides have y on so we'd be gathering everything together.
12. Re: How to make y the subject of these formulae?
a(2 + 3b) = 2bcd

I will make b the subject

2a + 3ab = 2bcd

2a = 2bcd - 3ab

2a = b(2cd - 3a)

13. Re: How to make y the subject of these formulae?
(Original post by multiplexing-gamer)
Ok thanks for the example. But both sides have y on so we'd be gathering everything together.
yes
14. Re: How to make y the subject of these formulae?
(Original post by TenOfThem)
yes
Thank you very much for the example, I will attempt the question soon and repot back!
15. Re: How to make y the subject of these formulae?
(Original post by multiplexing-gamer)
I've totally forgotten how to make y the subject.

How would I make y the subject of 2b=3(y+8)
You can rearrange anything when you consider that if two things are equal, then if you do the same thing to both sides, they are still equal.

So, the first step is to try and eliminate the 3 multiplying (y+8):

Therefore, diving both sides by 3, gives:

It's crucial you understand the concept here: this works because both things are equal to begin with, and so if I do the same to both things, they are still equal afterwards. Once you grasp that, then all these problems follow a simple recipe: if you have a multiplier you need to eliminate, you divide both sides by it, and if you have an addition (or subtraction) you need to remove, you subtract (or add) the number to both sides.

This skill is vital to your understanding of maths at a most basic level, so please do take the time to make sure you understand the concept here, which I shall repeat once again:
if two things are equal, then if you do the same thing to both of them, they are still equal afterwards.