Marta ate a quarter of a whole pie. edwin ate 1/4 of what was left. cristina then ate 1/3 of what was left. what fraction of the pie remains? I know the answer is 3/8 but I need the work cause I don't get how to do it

First of all, where'd you get 3/8? Change the denominators so they are 12, because the are the least multiple 3 and 4. You just added how much they ate, not what was leftover. So technically, they ate 7/12 of the pie. 12 - 7 = 5, so 5/12 is leftover.