OCR Stats 1 - Where do I start?Watch this thread
I got 87UMS in C1, and so far i'm getting generally 90%+ on papers on the stuff we've done (everything except integration and logs), so the fact that I could go from a brilliant A to something like a C (i'm sitting on Es in stats) is a huge concern, especially when everybody else finds it easy.
I also can't tell the difference between perms and combs.
Which other parts are you having trouble understanding? with permutations and combinations - think of the group of letters 'A B C D' - there are 4! permutations, because there are 4!=24 ways of arranging the four letters, in other words, the order of the letters is important here. You calculate it as "4P4" using the nPr button on the calculator.
But with combinations, there is only one combination - A B C D. The order that the letters are in is insignificant, whether is BACD, CADB... it's just those same four letters. You would calculate it as "4C4" using the nCr button on the calculator.
sorry if that seemed a little over-simplified - reading your post again, is it more that you can't tell the difference between perms and combs when given an exam question? or just in general?