Question says that a yogurt shop allows its customers to add, for no charge, 3 toppings to any yogurt purchased. Also the store has 15 possible toppings.
Now we need to find about how many different 3-topping combinations can a customers choose.
To find that we just need to apply combination formula
[tex]C(n,r)=\frac{n!}{r!(n-r)!}[/tex]
which is used to select r items out of n items
we have to find combination of 15 toppings into 3 toppings so we calculate C(15,3) using above formula
[tex]C(15,3)=\frac{15!}{3!(15-3)!}[/tex]
[tex]C(15,3)=\frac{15!}{3!*12!}[/tex]
[tex]C(15,3)=\frac{15*14*13*12!}{3!*12!}[/tex]
[tex]C(15,3)=\frac{15*14*13}{3!}[/tex]
[tex]C(15,3)=\frac{2730}{6}[/tex]
[tex]C(15,3)=455[/tex]
Hence final answer is 455.
