To solve this you need to change 3 and 2 1/2 into improper fractions so you get 6/2 and 5/2. Then you have to flip 5/2 so it becomes 2/5 and then you just have to cross cancel. Since the 2 from 2/5 can go into the 2 in 6/2 one time, 2/5 changes into 1/5 and 6/2 changes to 6/1. Now you can multiply across so 6 times 1 is 6 and 1 times 5 is 5 so you get 6/5. Now you have to change it into a mixed number which would be 1 1/5.
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!
