Respuesta :

We can write "n C r" as "C(n,r)" which is more function notation in style. 
C(n,r) = C(n,n-r) due to symmetry on Pascal's Triangle

Based on that rule
C(50,45) = C(50,5)
note how n = 50, r = 45, n-r = 50-45 = 5

Answer: Choice B