Stuck on simple formula rearranging

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andyuser727
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#1
Report Thread starter 6 years ago
#1
Hi

I'd be very grateful for any help. The question I'm trying to answer says :-

Rearrange the formula p(q-1) = q to make q the new subject.

The answer given is q = p/(p-1)

I don't understand how you get this answer...

Can anyone show the working please?

Thanks
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Notnek
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#2
Report 6 years ago
#2
(Original post by andyuser727)
Hi

I'd be very grateful for any help. The question I'm trying to answer says :-

Rearrange the formula p(q-1) = q to make q the new subject.

The answer given is q = p/(p-1)

I don't understand how you get this answer...

Can anyone show the working please?

Thanks
First expand the left-hand-side. Then move both 'q' terms to the same side. Then take out a factor of q.

Have a go at this and post all your working if you get stuck.
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andyuser727
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#3
Report Thread starter 6 years ago
#3
pq - p = q
pq - q = p
q(q - 1) = p
q = p / (q - 1)

OK excellent! Thanks. I still have questions tho. If you start substituting values for p and q, the formula looks wrong.

Eg. p = 2, q = 3
2(3 - 1) = 3
6 - 2 = 3
4 = 3 ?????
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Duke Glacia
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#4
Report 6 years ago
#4
(Original post by andyuser727)
pq - p = q
pq - q = p
q(q - 1) = p
q = p / (q - 1)

OK excellent! Thanks. I still have questions tho. If you start substituting values for p and q, the formula looks wrong.

Eg. p = 2, q = 3
2(3 - 1) = 3
6 - 2 = 3
4 = 3 ?????
take a look at the formulae (in bold)
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Notnek
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#5
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#5
(Original post by andyuser727)
pq - p = q
pq - q = p
q(q - 1) = p
q = p / (q - 1)
There are a couple of mistakes in your working and answer but they might be typos.

OK excellent! Thanks. I still have questions tho. If you start substituting values for p and q, the formula looks wrong.

Eg. p = 2, q = 3
2(3 - 1) = 3
6 - 2 = 3
4 = 3 ?????
This equation isn't true for any p and q. You seem to have picked random values for the variables and expected them to satisfy the equation.

If you're still not clear about this, please explain exactly what you mean.
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andyuser727
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#6
Report Thread starter 6 years ago
#6
pq - p = q
pq - q = p
q(p - 1) = p
q = p/(p - 1)

oops, sorry. Is that correct now?

I don't know why I was substituting random values. I get it now.

So if p = 3 then
q = 3/(3 - 1) then
q = 3/2
q = 1.5
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Notnek
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#7
Report 6 years ago
#7
(Original post by andyuser727)
pq - p = q
pq - q = p
q(p - 1) = p
q = p/(p - 1)

oops, sorry. Is that correct now?

I don't know why I was substituting random values. I get it now.

So if p = 3 then
q = 3/(3 - 1) then
q = 1 2/3
Yes that's correct now.
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