Henry, mom and the math homework

Henry was doing maths homework, saying to himself…
“2+5, the son of a b**ch is 7”
“3+6, the son of a b**ch is 9″
His mother heard this & asked, ” Henry ! What is this nonsense you are doing?”

“Oh Mom. Don’t disturb. I am doing my maths homework”
Mom: “Is this how your teacher taught you?”
“Yes mom ”

Infuriated mother picked up her cell phone and called the teacher:
“Are you teaching maths to children by saying… 2+2, the son of a b**ch is 4?”
There was silence for a moment
Then the teacher started laughing :
“What I taught them was… 2+2 THE SUM OF WHICH IS 4.”