Solve the problem of example 2.4 (page 51) by making use of the normal approximation to the binomial distribution and compare with the exact result.

Data from Example 2.4

A power station supplies power to 10 bulk consumers. They use power independently of each other and in random time intervals, which, for each customer, accumulate to 20% of the calendar time. What is the probability of the random event B that at a randomly chosen time point at least seven customers use power?