Suppose A and B are two rational numbers.
So A = p/q where p and q are integers and q > 0
and B = r/s where r and s are integers and s > 0.
Then A - B = p/q - r/s = ps/qs - qr/qs = (ps - qr)/qs
Now,
p,q,r,s are integers so ps and qr are integers and so x = ps-qr is an integer
and
y = qs is an integer which is > 0
Thus A-B can be written as a ratio of two integers, x/y where y>0. Therefore, A-B is rational.
no
Yes.
Yes.
Yes, it is.
Their count. Two in the first case, one in the second.
Yes.
Yes. The rational numbers are a closed set with respect to subtraction.
There is no number which can be rational and irrational so there is no point in asking "how".
Yes, that's true.
No.
Directly. Their difference IS the difference between them.
Yes. This is the same as asking for one rational number to be subtracted from another; to do this each rational number is made into an equivalent rational number so that the two rational numbers have the same denominator, and then the numerators are subtracted which gives a rational number which may possibly be simplified.