Chapter 6 - Section 6.4 - Permutations and Combinations - Exercises - Page 437: 30

$120$

There are 10 marbles in the big bag. We simply need to find the number of ways of choosing 3 marbles out of 10, which is $C(10,3)=\frac{10!}{3!(10-3)!}=\frac{10!}{3!*7!}=\frac{10*9*8*7*6*5*4*3*2*1}{3*2*1*7*6*5*4*3*2*1}=10*3*4=120$