ANSWER: 3/8
let's assume that Derrick is a nice guy and his pizza is an integer of 1
first he gave his friend a quarter so we subtract [tex]\frac{1}{4}[/tex] from 1
[tex]1-\frac{1}{4}[/tex]
now we rewrite 1 as a fraction with a denominator of 4 so that we're able to subtract: [tex]\frac{4}{4}-\frac{1}{4} =\frac{3}{4}[/tex]
now that Derrick still has [tex]\frac{3}{4}[/tex] of his pizza he's gonna give [tex]\frac{3}{8}[/tex] to his sister as well
meaning that we subtract again: [tex]\frac{3}{4} -\frac{3}{8}[/tex]
in order to be able to subtract different fractions, they got to have the same denominator, so we're going to multiply [tex]\frac{3}{4}[/tex] both numerator and denominator by 2: [tex]\frac{2*3}{2*4} -\frac{3}{8} = \frac{6}{8} -\frac{3}{8} = \frac{3}{8}[/tex]
we can now conclude that Derrick is left with only [tex]\frac{3}{8}[/tex] of his pizza.
