Explanation of the Solution

In the solution, how is it that
$$\frac{1}{4} $$of the pizza remains? Also, can someone please explain the solution to me (I think the answer is
NO
, as I got6
)? Thanks 
@responsibleraccoon Basically, we're trying to figure out how much of the pizza is left after Alice eats 2/3 of it, and Bob eats 1/4 of the remaining.
First, Alice eats 2/3 of the pizza this means that there is 1  2/3 = 1/3 of the pizza left. Of that 1/3 pizza (the "leftovers"), Bob eats 1/4 of it. That means, Bob eats (1/4) * (1/3) = 1/12 of the whole pizza.
Now, we can figure out the amount left after both Alice and Bob ate the pizza since Alice ate 2/3 of the whole pizza, and Bob ate 1/12 of the whole pizza, together they ate 2/3 + 1/12 = 8/12 + 1/12 = 9/12 = 3/4 of the whole pizza, leaving 1/4 of the pizza left.
So you would be correct that the answer is "no" here
Hope this helped, and let me know if I could clarify any part of it!

@audrey Thank you for the awesome explanation!

@aaronhma No problem!