Question

If a call is sampled at random, the conditional probability that the call is not "6+" minutes long given that it is a long distance call is:

Answer 1

I believe this problem has the following table for long distance call:

                                                0-1 minutes                        2-5 minutes                        6+ minutes

Long distance                            170                         120                         10

 

To solve this problem, let us first recall what probability means:

Probability = number of successful event / number of total events

 

In this case, an event is considered to be successful when the long distance call is not 6+ minutes long.  Therefore:

number of successful event = 170 + 120 = 290

 

Now the number of total events is the sum of all number of calls, hence,

number of total events = 170 + 120 + 10

number of total events = 300

 

Probability that the call is not 6+ minutes long is therefore:

Probability = 290 / 300

Probability = 0.9667

or

Probability = 96.67%