You can't, in "Show that" style ones you can't work back from the given solution. Well I mean you can in your head but then you have to write it down so that you end with it.
GCSE Maths question
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You can't, in "Show that" style ones you can't work back from the given solution. Well I mean you can in your head but then you have to write it down so that you end with it.
That isn't what it asked you to do though. Seems a few on here could do with a reminder about ensuring you read the question properly
you've got yourself very confused over this.... 1/3 is the chance of eating two orange sweet
there are 10 sweets in total not 10 yellow sweets but that is irrelevant anyway as the question is asking you to derive the quadratic equation from the information given not find the value of n
(chance of picking a yellow sweet first is 2/5 not 2/3 btw...)
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At work I expect people to do what they are asked to do not what they would like to do. This question seems to demonstrate quite well, judging from the comments here, that some people are unable to do this. Therefore, I think it's a good question and a good test for a working life!
It's not no reason, but sometimes they leave even the smallest bit of useful context out that some questions can be totally ambiguous.
you've got yourself very confused over this.... 1/3 is the chance of eating two orange sweet
there are 10 sweets in total not 10 yellow sweets but that is irrelevant anyway as the question is asking you to derive the quadratic equation from the information given not find the value of n
(chance of picking a yellow sweet first is 2/5 not 2/3 btw...)
Your correct, I skimmed question, my mistake.
It's easy no?
6/n * 5/(n-1) = 30/n(n-1) = 1/3 = 30/90
n(n-1) = 90
n^2 - n = 90
n^2 - n - 90 = 0
factorize
(n-10)(n+9) = 0
n = 10 or n = -9. you can't have -9 sweets. n = 10.
Fairly sure I did factorizing quadratics at GCSE so what is wrong with this question?
Edit: After reading a bit further you don't even need to factorize, just get up to the point before I said factorize.
6/n * 5/(n-1) = 30/n(n-1) = 1/3 = 30/90
n(n-1) = 90
n^2 - n = 90
n^2 - n - 90 = 0
factorize
(n-10)(n+9) = 0
n = 10 or n = -9. you can't have -9 sweets. n = 10.
Fairly sure I did factorizing quadratics at GCSE so what is wrong with this question?
Edit: After reading a bit further you don't even need to factorize, just get up to the point before I said factorize.
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This
I did think for a second you just smashed your kb against your forehead however.
Myself and numbers will never get along to that degree sadly.
Soldato
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fair point, it's been a while since the regimented 'you must do it this exact way i taught you any deviation loses marks' kind of exam
The question is used to demonstrate logical thinking and problem solving, which is virtually most of STEM careers.
Every now and then I have to do some integration at work, when designing building structures. So it does come up.
Why were they even complaining about this question? People say the exams aren't hard enough and then this happens and people think it is hard! I don't think it was hard enough! It should have at least asked what the probablility of two sweets without stating the answer already. Or even better define the probability in terms of n without giving the formula.
Its a 2 answer question IIRC - one asking you to demonstrate problem solving skills, etc. to get to n2-n-90=0 and then the 2nd part is to give n (which in itself is really easy to work out). (So you do need to work out what n is but there is more to it than that).
I actually found that bit the easier part :S - basically assumed as they were talking about sweets n would be positive and whole (integer) number, that n2 had to be bigger than 90 which meant n had to be bigger than 9.
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Wow, how could anyone struggle with that? Just an easy bit of algebra.
Soldato
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Wanna know the crank way of doing this?
n is the number of sweets in the bag.
n-1 is the number of sweets left in the bag after the first turn.
What is the total number of possibilities for our sweet draw as described?
n(n-1)
Now, Hannah eats the sweets; they aren't replaced nor does she add surplus sweets to the bag over what has been taken out. So the above expression remains constant.
n(n-1) = c
Expand the brackets and put the equation into the required form:
n^2 - n = c
n^2 - n - c = 0
Let's now find c for just the 6 sweets we know about!
36 - 6 - c =
c = 30
But hang on, that's only 1/3 of all possible outcomes accounted for the stage we are at. So the final expression is:
1/3(n(n-1) = 30
n^2 - n - 90 = 0
Partial marks, haha?
Part (b) is a doddle, but I expect the examiners do actually want you to show the steps of working the quadratic - the joys of school maths!
But the posters above are quite correct - Edexcel are looking for textbook knowledge of probability, counting and quadratics. They also want to see students doing basic modelling with algebra. As the bloke who did it for the BBC said, the difficulty lies in not pointing out the problem strategy, which is common in more routine questions where parts lead you through the required problem solving steps.
The question deserves to be on the higher tier paper.
n is the number of sweets in the bag.
n-1 is the number of sweets left in the bag after the first turn.
What is the total number of possibilities for our sweet draw as described?
n(n-1)
Now, Hannah eats the sweets; they aren't replaced nor does she add surplus sweets to the bag over what has been taken out. So the above expression remains constant.
n(n-1) = c
Expand the brackets and put the equation into the required form:
n^2 - n = c
n^2 - n - c = 0
Let's now find c for just the 6 sweets we know about!
36 - 6 - c =
c = 30
But hang on, that's only 1/3 of all possible outcomes accounted for the stage we are at. So the final expression is:
1/3(n(n-1) = 30
n^2 - n - 90 = 0
Partial marks, haha?
Part (b) is a doddle, but I expect the examiners do actually want you to show the steps of working the quadratic - the joys of school maths!But the posters above are quite correct - Edexcel are looking for textbook knowledge of probability, counting and quadratics. They also want to see students doing basic modelling with algebra. As the bloke who did it for the BBC said, the difficulty lies in not pointing out the problem strategy, which is common in more routine questions where parts lead you through the required problem solving steps.
The question deserves to be on the higher tier paper.
How have you overcomplicated it that much? That's not showing your workings, that's doing it in an obscure way.
you know that there are 6 orange sweets, so your probability is 6/n x 5/n-1
you've been told that it equals 1/3
you have 6/n x 5/n-1 = 1/3
you just multiply up by the denominators
so 6 x 5 x 3 = 1 x n x (n - 1)
90 = n^2 - n
0 = n^2 - n - 90
That is the full extent of working you would need to show, there's no knowledge of quadratics required, despite the result being one.
edit: if indeed you were asked to work out the answer in the next part of the question, that is where the quadratic would come in.
you know that there are 6 orange sweets, so your probability is 6/n x 5/n-1
you've been told that it equals 1/3
you have 6/n x 5/n-1 = 1/3
you just multiply up by the denominators
so 6 x 5 x 3 = 1 x n x (n - 1)
90 = n^2 - n
0 = n^2 - n - 90
That is the full extent of working you would need to show, there's no knowledge of quadratics required, despite the result being one.
edit: if indeed you were asked to work out the answer in the next part of the question, that is where the quadratic would come in.
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I used to be quite good at maths and received an A grade back in 2005.
I cant believe how much I have forgotten. I have no idea what you lot are talking about lol.
I cant believe how much I have forgotten. I have no idea what you lot are talking about lol.