I will try my best to explain but if you have questions on anything i say, ask me.
To solve #1 use example 3:
1) 4 blue/ 10 marbles X 6 red/10 marbles= 24 blue and red/20 marbles
answer: 24/20 --->(simplify) 3/5
2) example 1&2:
2red/10 marble
2/10 --> 1/5
answer: 1/5
3)2 blue/10 marbles
2/10 --> 1/5