First, let's find out how many 5/6 pound bags he can fill with on 2 pound bag.
2 divided by 5/6
2 x 6/5
2.4
He can fill 2.4 bags with one 2 bag.
Now we just need to multiply 2.4 by a number that will make it a whole number. You can use the guess and check method starting with 2 to figure your answer out, but 2.4 x 5 = 12 which is a whole number.
This means that Chad needs to buy 5 of the 2 pound bags to fill 12 of the 5/6 pound bags, and he will not have peanuts leftover