P(4) = C(10,4) .3^4 .7^6
C(10,4) = 10!/[4! 6!]
= 10*9*8*7/[4*3*2] = 30*7 = 210
so
P(4) = 210 * .3^4*.7^6
= 0.02
for the second part do that for
7 8 9 and 10 students and add results. Do not spend more that a week at it. If you get frustrated you can approximate a binomial distribution by a normal with
mean = n p = 10*.3 = 3
sigma^2 = np(1-p) = 10*.3*.7
= .21
so
sigma = sqrt .21 = .458
then use
http://davidmlane.com/hyperstat/z_table.html
The probability a pupil takes a bus to school is 0.3. If a sample of 10 pupils are chosen at random. Using binomial distribution. Find the probability that
a) exactly four pupils travel by bus.
b) more than six pupils travel by bus.
1 answer
1 answer