Question

Grandma makes chocolate chip cookies in batch of 100, and you choose one cookie at random. How many chips should she put in the dough so that the probability your cookie contains no chip is 0.02?

Answer 1

391 chips

Explanation:

This is a Poisson distribution problem with the formula;

P(X = k) = (e^(-λ) × λ^(k))/k!

Let n be the number of chips she puts in the dough.

Since she makes chocolate chip cookies in batch of 100, then the mean number of chips is n/100.

So, λ = n/100

Now, we want to find how many chips should she put in the dough so that the probability your cookie contains no chip is 0.02.

Thus;

P(X = 0) = (e^(-λ) × λ^(0))/0! = 0.02

This gives;

e^(-λ) = 0.02

Putting λ = n/100, we have;

e^(-n/100) = 0.02

-n/100 = In 0.02

-n/100 = -3.912

n = -100 × -3.912

n ≈ 391 chips