Question

How many of the 250 perch netted by a fisherman would you expect to have a mass more than 400g if the mass of the perch are normally distributed with a mean of 300g and a standard deviation of 80g.

Answer 1

400 is 100/80 = 1.25 standard deviations away from the mean. look up 1.25 in a cumulative normal distribution table (probably in your stats book). I get .8944. Meaning 89.44% of the time, each perch will be under 400g. Take it from here.