I can't really figure it out... Maybe I'm thinking about it wrong, but the only way I can see Mortimer's sister being twice her age when Mortimer is his father's age, would be if the father was 50. The closest I can get get is:
yah i got to that also lol and if u go with decimals 16.5 and 33.5 you would still never get to the exact number because it just keeps going lower and lower, so i dunno
well this kid i know said moritimer is 20 and sister is 30 and father is 50 and he said he got it right, so i guess i didn't understand it right or something, i'm gonna ask the teacher tommorow