Question

Find n(A) of the following set
A={101,102,103,104,...,121}

Answer 1

n(A) = number of items in set A

So how many elements are in set A?

Answer 2

In other words, how many whole numbers are there from 101 to 121?

Answer 3

21?

Answer 4

good, you got it

Answer 5

You can either count them out, or you can use the trick


Last number - First number + 1 = 121 - 101 + 1 = 21


Either way gives you a count of 21.