Thank for all the help on the previous subject, now got one on distribution..

In an examination it is known that the distribution of marks is N (52,24)

a) what proportion of the marks will exceed 55?

b) what proportion of the marks will be less than 45?

c) if a grade A is awarded for the to p5% of marks, what is the minimum mark required in order to achieve a grade A?

d) the bottom 20% of the marks was graded as an F, What was the range of these marks?

Sorry for all the questions, had hundreds of these and stuck on a few of them