Hi! I'm happy to help!
The recipe calls for 1/4 of a cup of cocoa, and we have 5/6 of a cup.
We use subtraction to solve for the difference:
5/6-1/4
To solve for this, we need to find a common denominator. We do this by finding the least common multiple of the two denominators we already have.
The least common multiple is 12, because that is the lowest number that both 6 and 4 are factors of.
We multiplied the 6 by 2 to get twelve, so, to make it equivalent, we have to multiply the 5 by 2 also.
10/12-1/4
Now, since we multiplied the 4 by 3 to get twelve, we need to do the same to the 1.
10/12-3/12
You never subtract denominators, only numerators. Now, all we have to do is 10-3:
10/12-3/12=
7/12
So, you would have 7/12 cup of cocoa left over if you made the cookies.
I hope this was helpful, keep learning! :D