The question is which sets of natural numbers are closed under addition. I know that odd is not, and I know how to prove that sets of multiples are, but my professor said there is something more and that is has to do with greatest common divisor. He said to pick numbers like 3 and 5 or 5 and 8...
Here is the question:
Consider the experiment of rolling two tetrahedra that are unfair in the sense that each has the following probabilities for each of the four faces:
P{1 dot}=1/10
P{2 dots}=2/10
P{3 dots}=3/10
P{4 dots}=4/10
Let X be the total of the outcomes in the two...