How many ways can a from be filled out?

Question

In a survey, viewers are given a list of 20 TV programmes. They are asked to label their three favourites 1, 2 and 3, and to put a tick against those they have heard of (if any) from the remaining 17. In how many ways can the form be filled out? (Assume that everyone has three favourite programmes to nominate.)

Answer 1

Choose favourite 1... $20$ ways

Choose favourite 2... $19$ ways

Choose favourite 3... $18$ ways

For each of the 17 remaining programmes decide whether or not to tick it... $2^{17}$ ways

So answer is $20*19*18*2^{17}$