instruction:
In this task, you are given two sets, and you need to count the number of elements at the intersection of two given sets.  A Set is shown by two curly braces and comma-separated numbers inside, like {1, 2, 3}. The intersection of two given sets is the largest set which contains all the elements that are common to both sets. To find the intersection of two given sets, A and B is a set consisting of all the elements common to both A and B.
question:
Set1: '{3, 4, 5, 6, 9, 17, 18}', Set2: '{3, 8, 9, 12, 13, 14, 15, 17, 18, 20}'. How many elements are there in the intersection of Set1 and Set2 ?
answer:
4


question:
Set1: '{1, 2, 3, 5, 7, 12, 13, 17}', Set2: '{16, 11, 20, 13}'. How many elements are there in the intersection of Set1 and Set2 ?
answer:
1


question:
Set1: '{19, 18, 11}', Set2: '{3}'. How many elements are there in the intersection of Set1 and Set2 ?
answer:

0


