The set {0, 1} is closed under which operation? (points : 3)
addition
multiplication
subtraction
none of the above

The set consist of numbers 0 and 1 so if we use any combination of those 2 numbers under some operation and get as result one of those 2 numbers that means set is closed under that operation.

for multiplication you get:

0*0 = 0
0* 1 = 0
1 * 1 = 1 
so all combinations used and answers are 0 and 1 which means set is closed under multiplication

It isnt for subtraction and addition because:
0-1 = -1

and 1 + 1 = 2