Probability first song is country is 3/7 probability second song is reggae is 2/6 which reduces to 1/3 probability of both is : 3/7 * 1/3 = 3/21 which reduces to 1/7 <==
To find the tip you have to change the percent into a fraction first. Since percent is out of a 100, 25% is 25/100 or 1/4. Multiplying 1/4 by 520 you get 130, which is how much the coach will tip.