|This tasty image was lifted from Fruitmagic|
A variation on that question came up again in the fifth grade in Michigan. "If Sandra has 12 oranges and Jim has 7 apples, how many pieces of fruit do they have combined?" I answered 19 and to my great astonishment, was struck down with zero ceremony or explanation.
It came up again in the seventh grade. "What is the sum of 39 apples and 23 oranges?" I answered 62, and was wrong again. I wondered if there was some unexplained prejudice against fruit.
In high school Mrs. Warnaar brought it up again, "Calculate the sum of 3 apples and 5 oranges". Of course I hadn't learned my lesson yet, and answered 8, but this time my teacher kind enough to explain that the correct answer was, "The sum of 3 apples and 5 oranges is 3 apples and 5 oranges". I felt appalled that trained professional math teachers would set up such a dirty trick.
By the time I got to college I was ready to slap the professor for again using fruit as a metaphor for an algebraic concept; at least this time I was wise to the trick and would substitute other things no one groups together like monkey wrenches, socks, batteries, rubber erasers,... and maybe steaks when I got in a food mood. Many problems in algebra were cleared up for me when I threw out the convention of mathematical fruit salad.
I won't be using fruit to teach my children math. Never again will I visit that chaos on a child's mind.