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!

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

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..

For b): http://www.mathsrevision.net/gcse/pages.php?page=1 Basically a over b - c over d = ad - cb over bd. My GCSE had a 10 mark question at the end of the paper on one of these (I think), I had to ask for extra paper...

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!

^ 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)

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!

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

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.

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 [1] And: n(x+12) = 720 => n = 720/(x+12) [2] Then subtracting [2] from [1] 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.

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.