Hi. Can someone explain the Bionormial equation to me . i know that Binormial means the probability of success over failure from what i have read and that the probability of success in each trial is the same threfore- we only use inormal is we want to fidn the probability of success of failure. in order to find the bionormal distribution we have to know the
n- total population
r- number of choices chosen
p- success
q-failure
and the equation is (this is what i type into the calculator) nCrqn-rpr (currently, i am just memorising this quation meaning that i dont know what is the purpose of C (combination) being in the bionormial question .
so far, i am doing alright by asnwering a few binormial question until i came across this one:
2. A particularly long traffic light on your morning commute is green 20% of the time that you approach it. Assume that each mornign represents an independent trial.
b) Over the next 20 mornings, what is the probability that the light is green on exactly four days?
my solution:
20C4x(o.8)^16x(0.2)^4 + 20C3x(o.8)^17x(0.2)^3 + 20C2x(o.8)^18x(0.2)^2 + 20C1x(o.8)^19x(0.2)^1
now this is wrong. the correct answer is : 20C4x(o.8)^16x(0.2)^4 = 0.218.
can someone please explain? i need to learn my statistics asap as my exam is by the end of the month