00:01
In this question, we are given an example of an extrasensory perception experiment, which is an experiment conducted by psychologist.
00:10
And in this experiment, the psychologist has 10 cards numbered 1 to 10, and she looks at the cards one at a time.
00:17
And when she looks at each card, the subject writes down the number that he thinks is on the card.
00:22
And so we're being asked to calculate a couple possibilities regarding this type of experiment.
00:28
So first, part a is asking how many possibilities are there for the order in which the subject writes down the numbers? so we're being asked basically how many ways are there to write down the numbers 1 to 10, how many different orders are there to do this? and so since we care about the order, we need to do a permutation, since the permutation deals with orders.
00:56
And so as a refresher, the permutation formula, so n permutation r is going to be n factorial over n minus r factorial.
01:10
And so since we have 10 total numbers and we are also ordering 10 numbers, we will do 10 factorial over 10 minus 10 factorial.
01:25
And remember that 0 factorial is 1, so we simply have 10 factorial possibilities as to how to order these objects...