simple rearranging thats got be baffled Watch

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thewebmaster
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#1
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#1
I dunno why but this has got be completely baffled, maybe its because i'm not thinking straight with all the revision but i just CANNOT get my head around this make p the subject.

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This is going to take someone 2 seconds however can they explain to me how they have reached their answer i get to...

(*100) 100A = 100P + PRT

then

(/RT) 100A/RT = 100p + p

then simplify

100A/RT = 101P

Where form here or have i gone total wrong way?
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roff
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#2
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100a = P + Prt
100a= P + P(rt)
100art = 2p
100art/2 = P
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Sparkling_Jules
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a = P + Prt/100
100a = 100P + Prt
100a = P(100 + rt)
P = 100a / 100 + rt
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Sparkling_Jules
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#4
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Remember when you divide or multiply something you have to do it to the whole equation.
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DaveManUK
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a=p+prt/100 [*100]
100a=100p+prt [factorise p]
100a=p(100+rt) [divide both sides by (100+rt)]
p=100a/(100+rt) [look the answer ]

------------------
edit: divide by 100 on top and bottom

p = a / (1 + rt/100) [see edit]
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DaveManUK
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(Original post by Sparkling_Jules)
Remember when you divide or multiply something you have to do it to the whole equation.
something which you did. :rolleyes:
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thewebmaster
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#7
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This is taken directly from the aqa mark scheme for that year. A TOUGHER question than it looks i think, i don't know what they're doing here and i thought your answer was right ramroff but this is just not the case with aqa always got to make things that much more dificult
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Sparkling_Jules
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(Original post by DaveManUK)
something which you did. :rolleyes:

Oops just spotted that and edited it.
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goku999
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A = P + Prt/100

A - P = Prt/100

100(A-P) = Prt

100a - 100P = Prt

100a = 100P + Prt

100a = P(100+rt)

100a/(100+rt) = P
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thewebmaster
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#10
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I am with people up until this point...

100a = P(100 + rt)
P = 100a / 100 + rt

what's the crack here, how can you just suddenly turn the 100a into 100a/100+rt and completely forget about the p just put on other side of = sign.

also afterwards when you change it to 1+rt what going on here?

Sorry for the backward nature of my question however this is something i've never come accross before, give me a quadratic anyday
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goku999
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(Original post by thewebmaster)
I am with people up until this point...

100a = P(100 + rt)
P = 100a / 100 + rt

what's the crack here, how can you just suddenly turn the 100a into 100a/100+rt and completely forget about the p just put on other side of = sign.

also afterwards when you change it to 1+rt what going on here?

Sorry for the backward nature of my question however this is something i've never come accross before, give me a quadratic anyday
Like i had wrote

100a = 100P + Prt

there is a common factor of P on the RHS

So u take that common factor which makes it to P(100+rt)
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DaveManUK
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(Original post by thewebmaster)
I am with people up until this point...

100a = P(100 + rt)
P = 100a / 100 + rt

what's the crack here, how can you just suddenly turn the 100a into 100a/100+rt and completely forget about the p just put on other side of = sign.

also afterwards when you change it to 1+rt what going on here?

Sorry for the backward nature of my question however this is something i've never come accross before, give me a quadratic anyday
read my post aboves
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Sparkling_Jules
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Step by step:
a = P + PRT/100
100a = 100P + PRT x100
100a = P(100 + RT) take the P out (factorise)
100a/(100 + RT) = P divide by (100 + RT)
P = 100a/(100 + RT)

was it the lack of brackets at the end that confused you?
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goku999
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#14
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There is 100 both on the numerator and the denominator divide by 100 to get 100A into jus one A
so 100A / 100 = A
100/100 = 1
rt/100 = rt/100

This gives u the answer
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thewebmaster
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#15
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Bit of a long winded question that one hope there isn't one on my exam.

What confused me was the fact there was the + sign and that means everything has to be multiplyed. Also i didn't see straight off the 100A/100+rt

then the divide by 1 i thought would be more complicated. i thought you were factorising or something when you had p = a/1+rt

Strange question. But thanks a lot everyone really helped me. Anyone fancy the other problem i'm stuck on, going through past papers and the bu**ers are just popping up at me everywhere.
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DaveManUK
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#16
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it wasnt that hard
expand /get rid of denominators
isolate and factor
divide factors through
further simplification
a bit more practise with the algebra you should be doing those with your eyes closed
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thewebmaster
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#17
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its the stupid questions likethis at the beginning that confuse me and make me waste time.

Then i don't have enough time to complete the paper and lose marks at the harder questions which i can do.

Does anyone have any links to dificult algebra i.e. the most dificult i will encounter at gcse level, thereby i can test myself and see if there are any techniques i don't know. The thing is i've only just come across the idea of algebraic fractions due to us having a slow class. This has caused me a lot of problems, i'll show you what i mean in another post sometime.
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Kirjava
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#18
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I don't know any links... but these questions always have the same method.

1) Remove any denominators. You've done this by multiplying by a 100. Easy.

2) Move all like terms (the ones containing what you want to make the subject) onto the same side of the equation. Easy again - treat things like 'PRT' as one term. I.e. if you're moving PRT, you put it on the other side as -PRT. You shouldn't split it up into P and RT. Move any that don't contain what you want to make the subject onto the other side. In this case, this stage is already done - all terms contain P are on the right, and all those that don't are on the left.

3) Factorise!

100A = 100P + PRT
becomes
100A = P(100+RT)

4) Then just move the brackets to the other side.

P = 100A/(100+RT)
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