1 - counting principles Flashcards
1
Q
produce principle
A
n(A AND B) = n(A) * n(B)
2
Q
addition principle
A
n(A OR B) = n(A) + n(B)
if mutually exclusive
3
Q
permute
A
the order they are chosen in matters
nPr = n!/(n-r)!
4
Q
combination
A
when order doesn’t matter
nCr = n!/r!(n-r)!
4
Q
exclusion principle
A
count what you aren’t interested in and subtract it from the total
eg how many 3 digit numbers don’t end in a 1
no. 3 digit no - no. 3 digit no that end in 1
5
Q
grouping objects
A
treat them as a single objects and remember to deal with the permutations within a group
6
Q
keeping objects apart
A
permute the remaining objects and insert the separated objects into the gaps
7
Q
repetitions
A
divide by the no. repetitions factorial
eg if you had 3 Es divide by 3!
8
Q
P(A) if all outcomes are = likely
A
no. outcomes of A / total no. outcomes
