 Anyone good at maths? | The Popjustice Forum

# Anyone good at maths?

Discussion in 'Pop & Justice' started by IotV, Mar 17, 2010.

1. Hey guys. Generally, I find maths quite easy, but whilst revising for my exam in June, I came across this, and genuinely don't have a clue. Would love if someone could put my mind at rest!

1. When the price of an apple rises by 12p, I can buy ten fewer for £7.20.
a) Let the price of an apple before the price rise be x pence.
Show that

720/x - 720/x+12 = 10

b) Find the price of an apple before the price rise.
A solution by trial and improvement will not be accepted.

Would be so, so, so thankful if someone could work it out!

2. I think I can work out a, but I need my calculator for that and I can't find it!

3. Are we solving for X? I got 24.

4. I would love you forever. Calculator on computer?

5. Oooh, thanks! Can you show me the working out, please? Want to learn it. Thanks!

6. 24 it is.
I sucked at maths, but this wasn't that hard. It was actually rather fun to do something like this again!

7. Now I feel stupid! Haha. Can you show me the working out, please? Thanks! And can anyone do b)?

8. B is 24.
After the rise the price 36..

I'll try to find a way to explain it, but I don't really know how to write it out in an understandable way..

9. I cheated and used an online quadratic equation calculator since I don't remember how to solve for the roots. But basically I:

moved the 720/(x+12) to the other side
720/x = 720/(x+12) +10

then multiplied everything by x
720 = 720x/(x+12) = 10x

then multiplied everything by (x+12)
720(x+12) = 720x + 10x (x+12)

720x + 8640 = 720x + 10x^2 + 120x

10x^2 + 120 x - 8640 = 0
x^2 + 12x - 864 = 0

and the roots were (x - 24) (x + 36)

probably not the easiest way to do it but it works!

10. I love you all so much, but especially Wowx4! Thanks!

11. ^ I used a different method.
720/x - 720/x+12 = 10
720(x+12) - 720(x) / x(x+12)=10
720x + 8640 - 720x / x^2+12x=10
8640/x^2 +12x = 10
8640 = 10x^2+120x
10x^2+120x-8640=0
x^2 + 12x - 864 = 0
(x-24)(x+36)

12. Thank god the hardest thing I had to do on my GRE's was something like finding the length of the radius of a circle.... Pi R Squared baby!

13. Everyone seems to have given the answer to b, but not to a. Was that the only part you were stuck on?

14. I don't really get why a is a question. It's just an algebraic set-up of the information that's been provided. I'm not quite sure how you can show 'getting to' that.

15. I agree, but that seems to be what they're asking. The best I can come up with is to deliberately force yourself to use a simpler formulation and reduce it to that formula. Maybe something like:

Let m be the number of apples you used to able to buy for £7.20
Let n be the number of apples you can now buy for £7.20

Then:
m*x = 720
=> m = 720/x 

And:
n(x+12) = 720
=> n = 720/(x+12) 

Then subtracting  from  gives:
m-n = 720/x - 720/(x+12)

But from the description, m-n = 10 so:

10 = 720/x - 720/(x+12)
Q.E.D

I've no idea if that's what they're after (it's a little while since my GCSE exams...) so I'd say that's worth checking with a teacher who actually knows the syllabus.

16. That's what confused me.

17. Is that 'A'? Thanks!

18. This reminds me how my Maths teacher always persisted I wrote down all my answers in full sentences, containing the question. So when the question was 'if 2 sides of a triangle are 4 and 6 inches how big is the 3rd side?" I had to write down "if 2 sides of a triangle are 4 and 6 inches, the 3rd side is... because...".
HATED it. Especially cause he seemed to only require it from me.