Find a ∩ b if a = {4, 7, 10, 13, 17} and b = {3, 5, 7, 9}.

{7}.

Explanation: The union of two sets is a new sets that contains all the elements that are at least in one of the sets (without repeating elements) for example {1, 2, 3}∪{2, 3, 4}={1, 2, 3, 4}. The intersection of two sets is a new set that contains the elements that are in both sets, for example: {1, 2, 3}∩{2, 3, 4}={2, 3}. In the given exercise we have an intersection of two sets, so the answer is the common elements in both sets, in this case the only common element is number 7 so:

{4, 7, 10, 13, 17} ∩ {2, 5, 7, 9} = {7}

The merge of two sets is a new set that has all the elements that are at least in one of the sets w/out repeating elements. The intersection of two sets is a new set that has the elements in both of the sets because {1, 2, 3}∩{2, 3, 4}={2, 3}. In this case the only common element is number 7 so: {4, 7, 10, 13, 17} ∩ {2, 5, 7, 9} = {7}.

the narrator closes the lantern tightly so the old man is

not awakened by the bright light

explanation: