Probability Flashcards
P(a|b)
(find % given table)
do that combined number / b column total
P(A|B^c)
(find percent given table)
do all but B in the A column / all but B in the total column
given 2 % numbers find it contains A or B
make ven diagram
P(AUB)
make probability /100
add the numerators
given 2 % numbers, find the probability that it contains A or does not contain B
make ven diagram
P(AUB^c)
numerator of fraction includes the number on the bottom of diagram and middle /100
given 2 percentages
ex- 40% dogs 32% cats 18% both
find the probability that they own A given B
P(A|B)
use formula: P(AandB)/P(A)
independent=
same %
given table
is A and B independent?
do P(A|B) = %
and P(A) = %
P(A)= total A / total
candy box has 20 chocolates. 14 soft, 6 are hard. Find the probability you pick 3 soft candies in a row
14/2013/1912/18
given 3 percent values
ex- a cancer test has sensitivity of 92%, specificity of 89%. assume 4% have cancer
what is the probability you have cancer?
do tree diagram
use formula
ex- P(actually have cancer|positive test)
P(A|B)/P(A)
(the first 2) / (1st)(pos)+(2nd)(pos)
soft candy question the 14/20 * 13/19… but they give you a probability
(probability)^(how many)
soft candy question the 14/20 * 13/19… but they give you a probability
what’s the probability that 1 is wrong
do (probability)^(how many)
then 1- that
given:
P(A)=
P(B)=
P(AnB)=
are A and B independent?
so P(A) times P(B)
if it equals the same as P(AnB) then yes independent
complete the two way table
when A and B are mutually exclusive
they dont occur at the same time so the top left corner is 0
complete the two way table
when A and B are independent
do A/total times B/total
then do that probability times the total
soft candy question the 14/20 * 13/19… but they give you a probability and dont give you how many
what’s the probability that the candy, test, whatever is not right
(1-A) times (1-B)
“the detectives found that 40% of the people with food poisoning went to a cocktail party on the second night of the conference”
do P(whatever)
F=got food poisoning
A= attended party
P(A|F)
probability that they attended the party was 40% given they got food poisoning
given:
P(A)=
P(B)=
what is P(AuB)
do A+B - P(AnB)
P(AnB)=multiply A and B
what can you compare to P(A|B) to see if its independent
P(A) and P(A|B^c)
discrete random variable
YES gaps (NO decimals)
1, 2, 3, 4
continuous random variable
NO gaps (YES decimals)
1, 1.1, 1.2
P(X>=3)
add numerators / total
how to calculate mean
E(x)= X(P%)+X(P%)+x(P%)
how to calculate mean/SD in calculator
stat, edit, 12345 and probability, stat calc edit, L1, L2, calculate
how to describe mean
“If I choose many many ___(ppl, gum)___ , the average number of __(ppl, gum)__ in __fam, pack___ will be ___
How to describe SD
The number of __(ppl, gum)__ typically varies __#___ (ppl,gum) from the mean __#__ (ppl, gum)
X: 1, 5, 7 , 10
P: 3/23, 4/23, 4/23, 9/23
it this discrete or continuous
discrete
percentages on graph
.1, 2.1, 13.6, 34.1
graph: what is the probability that they do more than 20
do 20- mean
that answer is z score
find that on chart
if right side shaded, 1- that
move decimal into %
if youre adding a constant in your formula T=Y+4
then how would the mean and SD change
mean would add by 4
SD would stay
shape would stay
can u calculate the total mean of 2 variables that already have means by just adding their means together
yes, can be independent or dependent and will work
can you calculate the total SD of 2 variables that already have SD by adding them ^2 together and square root
if independent- yes
if not independent- no
How do you find SD of 2 variables that are already given SD and are independent
square them, add them, then square root
what does independent random variable mean
X has no relation to the outcome of Y
X= test score from grade 9
Y= test score from grade 10
are these independent random variables
yes because one grade does not help us predict the grades of another grade
what do you put in calc to calculate a binomial with x>4 versus x<4
x>4 then 1-binomcdf
x<4 then binomcdf
what do you put in calc to calculate a binomial with x>=4
then 1-binomcdf(n,p, 3)
“at most 3”
x<=3
