Hey sakuraxkisu.

For these kinds of problems you need to think about the distribution.

We know that for independent variables the distribution of P(A and B) = P(A)P(B): In this case A corresponds to one piston fitting and B corresponds to another piston fitting.

So if you find the probability of one piston fitting, then as long as every piston has the same distribution, you can raise this probability to the power of 100 to get the final probability that every single piston fits.

Its just based on the inductive definition of independence where the three variable case is P(A and B and C) = P(A)P(B)P(C)