A calculator contains four batteries. With normal use, each battery has a 90% chance of lasting for one year. What is the probability that all four batteries will last a year?

This is a binomial experiment.

_nC_x p^xq^n-x

Let n = 4

Let p = 0.9

Let x = 4

Let q = 0.1

Find the probability of x successes in n trials for the given probability of success p on each trial.

x = 2, n = 5, p = 0.25

A scientist hopes to launch a weather balloon on one of the next three mornings. For each morning, there is a 40% chance of suitable weather. What is the probability that there will be at least one morning with suitable weather?

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(p + q)ⁿ

n = 3

p = 0.4

q = .6