explain whether the following given are closed under addition:

B={0, 1}
T={0, 4, 8, 12, 16, ...}
F={5, 6, 7, 8, 9, 10,...}
{x|x E W and x>100}

3 answers

B clearly not, since 1+1=2, which is not in B

T clearly, since adding any two multiples of 4 yields another multiple of 4.

F yes, since adding any two integers yields another integer greater than 4.

No idea. What is W?
the "E" is one of the weird looking e's for math. The "W" is in italics.
If 4 plus 5 equals 9 is the set closed under whole numbers and addition?