a) The mean of a normal distribution is also the median. Half the population will have values above the mean. Half of 200 is 100, so ...
... 100 students will have grades above 70%.
b) 84% is 14% above the mean. Each 7% is 1 standard deviation, so 14% is 2 standard deviations above the mean. The empirical rule tells you 95% of the population is within 2 standard deviations of the mean, so about 5% of students (10 students) got grades higher than 84% or lower than 56%. The normal distribution is symmetrical, so we expect about 5 students in each range.
You basically have to divide 10/3 which will give you a decimal 3.3 so that would be your unit rate PER each box. Just multiply 3.3 by the number of boxes.
