Phuong and her friends attend a music festival, with a mix of rock and dance music. There are 22 friends altogether (including Phuong) and their attendance is as follows: . 13 attend the rock music 11 attend the dance music 4 attend both The values a, b and c represent the number of friends. rock dance a. Find the values of a, b and c. (3 marks) a = and c = b. The number of friends that attend either rock or dance, but not both is (1 mark) c. An friend is selected at random. The probability that they attend rock but not dance correct to 2 decimal places is (1 mark)