Question 981070
There are two ways to have a match with 2 drawn:
Probability both red = (4/8)*(3/7)=(12/56), as you wrote.
And same for blue, so sum is (24/56) as you wrote.  

yes, 100% probability if 3 are drawn.

The 4 draws can be
RRRR (24/1680)=(1/70)
RRRB
RRBR
RRBB
RBRR
RBRB
RBBR
RBBB
BRRR
BRRB
BRBR
BRBB
BBRR
BBRB
BBBR
BBBB Same (1/70) probability
So the answer is their sum, or (2/70).