The table gives the frequency distribution of marks obtained by a group of students in a test.

Marks	3	4	5	6	7	8
Frequency	5	x - 1	x	9	4	1

If the mean is 5,

(a) Calculate the value of x;

(b) Find the : (i) mode ; (ii) median of the distribution.

(c) If one of the students is selected at random, find the probability that he scored at least 7 marks.