A 1st grader was doing math aloud something like this:
"1, 2 sonofabitch is 3"
"2, 4 sonofabitch is 6"
"4, 1 sonofabitch is 5" etc.
Dad heard it and got upset and asked the child why he was saying that bad word. The child said that's how his teacher taught him math.
Dad talked to the teacher and found that his child had misunderstood the phrase 'sum of which'.