Answer:
The probability that a call last between 4.2 and 4.9 minutes is 0.4599
Step-by-step explanation:
Let X be the length in minutes of a random phone call. X is a normal distribution with mean λ=4.2 and standard deviation σ=0.4. We want to know P(4.2 < X < 4.9). In order to make computations, we will use W, the standarization of X, given by the following formula
We will use , the cummulative distribution function of W. The values of
are well known and the can be found in the attached file
We conclude that the probability that a call last between 4.2 and 4.9 minutes is 0.4599