Im having issues understanding this..can someone please help

4. In a class, 30% of the students study math (M) and science (S). 70% of the students study math (M). What is the probability of a student studying science(S) given he/she is already studying math (M)? 5. A single coin is tossed 5 times. What is the probability of getting at least one head? 6. What is the probability of the occurrence of a number that is odd OR less than 5 when a fair die is rolled