More Fun Than a Workbook
Kitten would rather do almost anything than her math workbook. Not that it’s a bad workbook, as that sort of thing goes, and our Buddy Math program has definitely helped her attitude. Still, whenever she can think of an excuse to do something else…
This time, the excuse was that she got the challenge problem at the bottom of the workbook page right — but when I tried to check her answer, I got it wrong. I explained to her my most frequently committed stupid math error: I always skim over those little words that can totally change a problem, like the word not.
So she made up a puzzle to help me practice watching for the little word.
Denise Gaskins' Let's Play Math 
30 balls are NOT green.
35 are NOT green.
Greg likes red and green balls.
Greg likes 40+ 10 -20 balls ( = 30)
There are the same number of red and green balls.
There must be 15 red and 15 green balls.
There are 50 balls (red, blue or green) altogether.
15 red, 15 green, 20 blue.
Non-green = 15 red + 20 blue = 35 total