porcupinetree
not actually a porcupine
- Joined
- Dec 12, 2014
- Messages
- 664
- Gender
- Male
- HSC
- 2015
did someone say hsp
depends, were you haram dingo that gets tomato sauce?did someone say hsp
I think you're confusing me with @ekmandepends, were you haram dingo that gets tomato sauce?
well in that case you're all g.I think you're confusing me with @ekman
holy trinity for lyf
Mostly correct, except the last line should have the 2's multiplied instead of added. Well done.For those who can't do the question here is what i did (may be wrong) :
a) First we choose k numbers out of the n and the out of the remaining n - k numbers we chose m - k of them since total selected is m.
b) Consider all possible combinations. Firstly if bob selects 0 cards, then when bob selects 1 card, , and so on up to when he picks all m.
EDIT: So first we pick the m cards and then decide whether or not to put them in one of two places.
[]
Ahh that was basically what I was thinking
EDIT: So first we pick the m cards and then decide whether or not to put them in one of two places.
[]
Well done, this was the "or otherwise" method. Though my expectation was that students would do it the other way around.Alternative method for part b:
The two marks was aimed at the combinatoric proof. If students could not see how to prove it combinatorically, I gave them the option of proving it from scratch algebraically (as you did). A bit more work than for 2 marks, yes. But better than receiving no marks because they are forced to use only one technique.A bit heavy for two marks though.
Not really if you argue how the result holds in terms of the arrangements in the question.A bit heavy for two marks though.
Nice work. Certainly quicker than the approach I showed previously.Not really if you argue how the result holds in terms of the arrangements in the question.
Even then, algebraically you just need to show is that