The probability that the next page she turns will contain an advertisement is 40%.
there are 384 of the 960 pages that contain an advertisement.
Now we find the probability that the next page she turns will contain an advertisement
that probability of an event is defined as:
Proabability=(Number of favourable outcome)/(Total number of outcome)
As total number of outcome=960
and number of favourable outcome=384
Then the probability that the next page she turns will contain an advertisement is given by 384/960 = 0.4
