The only way for a triangle to be made, the 2 smallest side lengths must be greater than the longest side length. So for A through C, the smallest sides diden't add up to the longest side, therefore D is the only correct answer.
The answer is 2 in 20 or 1 in 10, all you have to do is add up the total number of marbles and then have the number of yellow in the total. So 2 in 20. Hope this helps you!
