Just What I Needed

I was visited by The Math Fairy again last night. Erika was working on multiplying and dividing mixed numbers, you know, like 6 and 5/8ths times 3 and 2/5ths. She had spent hours on the worksheet, and apparently an entire pencil. She handed me the worksheet saying, “I only need the answers because I’ve already done the work,” apparently missing how these two things should be correlated.

I looked at the first problem and at her fruitless “work” and, wow, she took a wrong turn somewhere. By glancing at the problem I could tell that the answer was between 18 and 21 but her ciphering had yielded 42 trillion and change. It was like driving from Fort Worth to Dallas and winding up in Radio-free Nevada. Or Topeka. Bad example.

Back to the math. On a fresh sheet of paper I suggested that we start over. I asked how she had been taught to do this and she recited a three-word statute: keep-flip-change. Look, I don’t speak new math. The only way I know how to do this is convert the mixed numbers to improper fractions and then multiply the numerators and then the denominators. I showed this to her and she said, “That is ‘keep.’” I deduced that the flip-change had to do with division, and we proceeded to figure out the answers. I noticed that she was only transferring the answers to her sheet and drawing a box around them. I asked about showing her work and she reminded me, “I already did the work; I just need the answers.”