Since David starts out with 3 1/2 cups of blueberries and uses 1/4 cup to make a smoothie, we will need to subtract 1/4 from his starting amount of 3 1/2
David now has 3 1/4 cup of blueberries
David then uses half of this new amount of blueberries to make his pancakes. We will need to divide by 2 in order to figure out how much half is
First we can turn 3 1/4 into an improper fraction to make it easier to work with → 3 1/4 = 13/4
Now dividing 13/4 by 2 gives us
David used 13/8 cups of blueberries to make his pancakes
Turning this back into a mixed number leaves him with 1 5/8 cup of blueberries