To find how many pizzas only have cheese on them, you'll need to divide the number of pizzas ordered by 3. You'll need to divide the number of pizzas by 3 because 1/3 of the pizzas have cheese on them so by dividing 48 by 3, you'll be finding 1/3 of the pizzas w/ cheese.
48/3=16
Once you've divided 48 by 3, you'll get 16 pizzas w/ cheese.
We know that The formula for combinations is C=n!/[(n-r)!*r!] where n is the total number of objects you choose from r is the number that you choose to arrange
in this problem n=15 students r=4 students C=15!/[(15-4)!*4!]-----> C=15!/[11!*4!]---> (15*14*13*12*11!)/(11!*4*3*2*1) C=(15*14*13*12)/(24)----->C=1365
