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# AQA A2 Mathematics MPC4 Core 4 - 9th June 2015 [Discussion & unofficial markscheme] watch

1. (Original post by CD223)
What I wrote on the mark scheme was what I put down in the paper so I'm hoping I got the majority right but probably missed some method marks - 71-72 maybe?

Core 4 will be hard

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thats great for you then! I'm just worried Bath won't let me in if I don't get that A* in Maths it's annoying as they've increased the grades I need from AAB to A*AA I know just hopefully not as hard as this exam! :/
2. (Original post by UOE15)
Yeah I do understand what you've done, it is logical but I just don't think I'd remember how to do it in the exam haha
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Haha just keep attempting past questions on differential equations until you're confident?
3. (Original post by HennersPD)
thats great for you then! I'm just worried Bath won't let me in if I don't get that A* in Maths it's annoying as they've increased the grades I need from AAB to A*AA I know just hopefully not as hard as this exam! :/
Seems harsh?!

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Haha just keep attempting past questions on differential equations until you're confident?
Yeah I am going to do that as I did that for vectors and can vaguely do them now!
5. (Original post by CD223)
Seems harsh?!

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I know that's why I'm panicking about getting an A* now as I'll need 100 UMS in core 4 as i only think I've got about 64/75 in core 3 can you suggest any tough vectors questions as thats what I'm worst on!
6. 5b Jan 11 explanation anyone?
7. (Original post by amyrah)
5b Jan 11 explanation anyone?
Yeah, so it's just saying that when t=d, m = m0/16.

i.e. 10/16 = 10 x 2^(-1/8)d

=> 1/16 = 2^-d/8 (as the 10's cancel)
8. (Original post by datpr0)
Yeah, so it-s just saying that when t=d, m = m0/16.

i.e. 10/16 = 10 x 2^(-1/8)d

=> 1/16 = 2^-d/8 (as the 10's cancel)
So basically I can put any value as m0?
9. Could someone explain q7 from June 11 for me please :/

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10. (Original post by amyrah)
So basically I can put any value as m0?
Well yes, because the values you enter would just cancel each other. I think, actually a better way of showing it mathematically would be to just indicate the m0's cancelling.
11. Could someone explain q7 from June 11 for me please :/

EDIT: also 8b of the same paper. Why is it + 1/(1-x) as I keep getting minus. Also how do you change to the form they want the answer in

Thanks!
12. (Original post by EmilyC96)
Could someone explain q7 from June 11 for me please :/

EDIT: also 8b of the same paper. Why is it + 1/(1-x) as I keep getting minus. Also how do you change to the form they want the answer in

Thanks!

This is 8b. I did it a few days ago too and was confused by it but apparently you multiply the -1 by (-x/1-x) to get (x/1-x). Well that's what my teacher said anyway.
Hope that helps
13. (Original post by EmilyC96)
Could someone explain q7 from June 11 for me please :/

EDIT: also 8b of the same paper. Why is it + 1/(1-x) as I keep getting minus. Also how do you change to the form they want the answer in

Thanks!
7
a) basically rewrite what they've told you in a differential equation.

They said surface area (A) is decreasing at a constant (-k) rate (t).
=> dA/dt = -k

... dA/dt is the rate of change of surface area. It is DECREASING at a CONSTANT rate, so -k.

b) i. Integrate your differential equation.

=> A = -kt +C

Its INITIAL (t=0) radius is 60cm so C = 4pi x 60^2 (as they tell you to assume surface area = 4pi x r^2).

With C calculated, input the values they give you and C into the integrated equation. This gives:

4pi x 30^2 = -9k + 4pi x 60^2

Solve to find k.

Substitute k & C into integrated equation and just take 1200pi out as a factor to get it in the correct form.

b) ii. A = 0, => -t + 12 = 0...
14. (Original post by EmilyC96)
Could someone explain q7 from June 11 for me please :/

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Thank you!!

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This is 8b. I did it a few days ago too and was confused by it but apparently you multiply the -1 by (-x/1-x) to get (x/1-x). Well that's what my teacher said anyway.
Hope that helps
Thanks

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17. Anyone fancy explaining the necessary and sufficient notations?

According to the spec we need to be able to use and understand them.
18. Guys I will be really grateful , if someone helps me with a question, I attempted it like 10 times and don't know what to do.
Its a question from JUNE 2010 QUESTION 3(b)
Thanks !
19. Could someone help me with 3c from jan 12 please

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20. (Original post by EmilyC96)
Could someone help me with 3c from jan 12 please

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It's pretty simple actually.

Cubed-root of 100 = 10^2/3

Therefore just consider what value of x is required for 8 + 6x = 10 to be true. Then substitute this value of x into your answer to b and simplify into the form a/b.

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