Intro to stats and anayltics

Question

If a seed is planted, it has a 80% chance of growing into a healthy plant.

If 7 seeds are planted, what is the probability that exactly 2 don't grow?

Round your answer to 4 decimal places.

Can you write the excel formula for me?

Answer 1

Hi Lucy,

I don't know the Excel formula, but you can compute this probability with a calculator relatively easily. This is a binomial distribution with "success" (ironically non-growth) and "failure" (ironically growth). Binomial distribution formula:

P(X=x)= C(n,x) p^x * q^n-x

C(n,x) = n!/(x!(n-x)!)

!=Factorial=4*3*2*1, etc.

n=sample size

x=number of "successes" you desire

p=probability of success

q=probability of failure=1-p

Here:

n=7

x=2

p=0.2--probability of non-growth

q=0.8--probability of growth

P(X=2)=C(7,2)*0.2²*0.8⁵

C(7,2)= 7!/(2!*5!) = 21

P(X=2) = 21*0.2²*0.8⁵

P= 0.2753

I hope this helps.