In a study to examine helping behaviour, we ask an elderly woman to pretend to collapse on the main road. We count the number of people that walk by before assistance is rendered. We repeat the...

In a study to examine helping behaviour, we ask an elderly woman to pretend to collapse on the main road. We count the number of people that walk by before assistance is rendered. We repeat the procedure 2 000 times over a period of a year. The data are normally distributed, with a mean of 20 and a standard deviation of 5.

a) If we assume that this is the data for the population of cases of helping behaviour, what is the probability that at least 35 people will walk past an elderly woman who collapses on the main road?

b) What is the 25th percentile of ‘helping behaviour’?