05-06-2015, 04:36 PM
1
Maths problem.
Earlier this week this question was in the Edexcel Maths GCSE paper:There are n sweets in a bag. 6 of the sweets are orange. The rest of the sweets are yellow.
Hannah takes a random sweet from the bag. She eats the sweet.
Hannah then takes at random another sweet from the bag. She eats the sweet.
The probability that Hannah eats two orange sweets is 1/3.
Show that n² – n – 90 = 0.
A students response to this on Twitter was:-
"Hannah eats some sweets" OK "Calculate the circumference of the moon using your tracing paper and a rusty spoon"
Kind of restored my faith in today's young students.
05-06-2015, 09:50 PM
4
Re: Maths problem.
This is easy peasy... not like the proper questions we had in 'O' level.....Right, there are 6 orange sweets in a bag containing N sweets, so the probability of choosing an orange sweet is 6/N.
Picking a second sweet there are 5 orange sweets in a bag of N-1.
The combined probability of these events happening are 6/N x 5/(N-1).
We know that this = 1/3 so we get 6/N x 5/(N-1) = 1/3
or 30/ (N² – N) = 1/3 which can be rearranged to n² – n – 90 = 0.
QED
Come on, what do people want these days, to be given the answer on a plate?
05-06-2015, 10:07 PM
5
Re: Maths problem.
Originally Posted by Meg
->
Algebra ....Mmmm no thanks I will pass
I decided it was pointless when I was at school and I would never use it and I never had. Glad I didn't clutter up my brain with unnecessary things
.
05-06-2015, 11:15 PM
7
Re: Maths problem.
Originally Posted by Grumblewagon
->
This is easy peasy... not like the proper questions we had in 'O' level.....Right, there are 6 orange sweets in a bag containing N sweets, so the probability of choosing an orange sweet is 6/N.
Picking a second sweet there are 5 orange sweets in a bag of N-1.
The combined probability of these events happening are 6/N x 5/(N-1).
We know that this = 1/3 so we get 6/N x 5/(N-1) = 1/3
or 30/ (N² – N) = 1/3 which can be rearranged to n² – n – 90 = 0.
QED
Come on, what do people want these days, to be given the answer on a plate?
*SCREAMS and hides head in bucket*
05-06-2015, 11:21 PM
8
Re: Maths problem.
Originally Posted by Grumblewagon
->
This is easy peasy... not like the proper questions we had in 'O' level.....Right, there are 6 orange sweets in a bag containing N sweets, so the probability of choosing an orange sweet is 6/N.
Picking a second sweet there are 5 orange sweets in a bag of N-1.
The combined probability of these events happening are 6/N x 5/(N-1).
We know that this = 1/3 so we get 6/N x 5/(N-1) = 1/3
or 30/ (N² – N) = 1/3 which can be rearranged to n² – n – 90 = 0.
QED
Come on, what do people want these days, to be given the answer on a plate?
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