Check your sig figs rules, since your answer should have as many sig figs as the value given with the LEAST amount of sig figs. (50.0m) Hence, the answer is 115000 (3 sig figs).
Re: 2015 permutation X2 marathon
You can think of it as this way: If the player picks the door with the goat initially P(G)=\frac{1}{3} and switches, his chances of winning the goat is 100%. Since the probabilities of which of the two doors with the car behind it do NOT change and that the...
If you fall slightly behind the published cut-off and there are any vacancies available (extremely unlikely for UNSW commerce), you might receive an offer.
Everyone mistakes them (even uni lecturers screw up their arithmetic from time to time), practice a-lot to minimise the amount of care-less mistakes you make.
You don't have to use matrices to do the cross product.
If you have vectors u=a+b+c and v=i+j+k.
You can do u x v =<bk-cj,ci-ak,aj-bi>
Using this to evaluate the cross product you should get u x v = 5i-4j+k.