UKC

I know lots of you will be able to do this with your eyes closed . I should be able to but think I’m wrong . 
y is inversely proportional to d sqr

when d= 10 y= 4

d is directly proportional to x sqr 

when x = 2 , d = 24 

find a formulae for y in terms of x 

give your answer in its simplest form .

I won’t post what I think as it “ feels “ wrong . Asking for eldest  boy child  . 

In reply to mike123:

The above doesn't "smell" like a GCSE maths question.  Can you post the actual question please.   (I'm not a maths teacher, but son did GCSE maths in summer and was helping him revise so have a feel for how they sound)

In reply to mike123:

I’ll take a stab at y = 6xsq/25.

jcm

In reply to mike123:

y = k  / (d^2)

Thus k = (d^2)y, k= (100)4 = 400

d = m x^2

Thus m = d/(x^2) = 24/4 = 6

So y = 400 / d^2, d = 6 x^2

So y = 400 / (36 x^4) = 100 / (9 x^4)

I think...

In reply to mike123:

It's grade 8, perhaps 9.

Solution:

In reply to Jamie Wakeham: brilliant  thanks Jamie . And thanks all . He is predicted a 9 and was annoyed he could not do it

In reply to mike123:

Which spec, out of interest?

An awful lot of the questions that are designed to distinguish between grades 8 and 9 are bit like this in character - maths that he will know how to do, but applied in an unusual way (or, sometimes, two seemingly disparate areas that you have to be able to connect up).  It's about testing the ability to think on the fly, to make up a way of solving something you've not seen before.  So he'll want to do as many of this type of question as possible!

In reply to Jamie Wakeham: thanks for that . I’m out at the moment but it’s on of the edexcel specs , not sure which . It’s a full paper and he had done  all the other  questions . I  will make sure to get as many papers as possible . He found all the other questions more or less straightforward. 

In reply to mike123:

As Jamie says the current papers only have one or two questions like this. I wouldn't normally recommend this, but if he wants more of this type of questions, and is confident, the early Edexcel specimen papers, prepared before the specification change in 2015? , have a number of these type of challenging questions. Be warned though at the time I had a couple of students who got A*'s in year 10 and had started AS maths. They were getting around 30/80 on these papers.