There are 30 scouts and 20 guides in a school. In another there are 20 scouts and 15 guides.From each school one student among them is to be selected for participation in a seminar.
What is the total number of possible selections?

There are 20 girls and 15 boys in a class. (b) What is the ratio of number of girls to the total number of students in the class ?

A class has 15 students whose ages are 14, 17, 15, 14, 21, 17, 19, 20, 16, 18, 20, 17, 16, 19 and 20 years. One student is selected in such a manner that each has the same chance of being chosen and the age X of the selected student is recorded. What is the probability distribution of the random variable X? Find mean, variance and standard deviation of X.

Of the students in a college, it is known that 60% reside in hostel and 40% are day scholars (not residing in hostel) . Previous years results report that 30% of all students who reside in hostel attain A grade and 20% of day scholrs attain A grade in their annual examination . At the end of the year, one student is chosen at random from the college and he has an A grade, what is the probability that the student is a hostler ?