# Rearranging FormulaeWatch

#1
I don't really understand how to rearrange formula e,our teacher taught the method when you put arrow then do it the other way again.

Question, If p=5L change the subject of the formula to L. Hence find L when P=73
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1 year ago
#2
(Original post by SBizzy)
I don't really understand how to rearrange formula e,our teacher taught the method when you put arrow then do it the other way again.

Question, If p+5L change the subject of the formula to L. Hence find L when P=73
There must be a little more to the question. p + 5L isn't an equation - it must be equal to something. Or do you mean p = 5L?
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#3
(Original post by Pangol)
There must be a little more to the question. p + 5L isn't an equation - it must be equal to something. Or do you mean p = 5L?
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1 year ago
#4
(Original post by SBizzy)
If p = 5L, then you find the value of p by multiplying L by 5. Think of L as the price of a light bulb, and p as the total cost of five of them. If you know the price of one light bulb (L), you can work out the total price by multiplying by 5. But suppose you knew the total price (p) - suppose this is £10. How much would each 5 of the light bulbs cost? How have you worked this out?

(I know it would be very easy to just give you the answer to your original question, but if you can follow this through, you should be able to do the same thing again and again in other questions.)
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#5
(Original post by Pangol)
If p = 5L, then you find the value of p by multiplying L by 5. Think of L as the price of a light bulb, and p as the total cost of five of them. If you know the price of one light bulb (L), you can work out the total price by multiplying by 5. But suppose you knew the total price (p) - suppose this is £10. How much would each 5 of the light bulbs cost? How have you worked this out?

(I know it would be very easy to just give you the answer to your original question, but if you can follow this through, you should be able to do the same thing again and again in other questions.)
Would it be £2 each?
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1 year ago
#6
(Original post by SBizzy)
Would it be £2 each?
Yes - and now you can see that you have to divide by 5, which is the opposite to multiplying by 5.

If you want to do this with algebra, the golden rule is to always do exactly the same thing to both sides of the equation. In this case, that thing is "divide by 5". So, we go from p = 5L to p/5 = 5L/5. and of course, if we take L, multiply by 5 to get 5L, and then divide by 5 again, we get right back where we started, so 5L/5 = L, and you end up with L = p/5.
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#7
(Original post by Pangol)
Yes - and now you can see that you have to divide by 5, which is the opposite to multiplying by 5.

If you want to do this with algebra, the golden rule is to always do exactly the same thing to both sides of the equation. In this case, that thing is "divide by 5". So, we go from p = 5L to p/5 = 5L/5. and of course, if we take L, multiply by 5 to get 5L, and then divide by 5 again, we get right back where we started, so 5L/5 = L, and you end up with L = p/5.
Still struggling with this homework...
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1 year ago
#8
(Original post by SBizzy)
Still struggling with this homework...
Not easy to know what to say considering the only question you have posted has been answered...
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#9
(Original post by Pangol)
Not easy to know what to say considering the

only question you have posted has been answered...
I'll just stop doing it, thanks for your help!
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