From Bedtime Math:
Big kids: The record distance for a thrown boomerang to travel is 1,401 feet. If it traveled exactly 1,401 feet on the return trip too, how many feet did it travel in total? Bonus: Meanwhile, the longest Frisbee throw is 1,333 feet – about a quarter of a mile! How much farther from the thrower did the boomerang travel than the Frisbee?
From the submitter, who sends in the thinking of two of his students:
(1) first student, having doubled the boomerang distance in the earlier question, now doubles the frisbee distance and calculates (2801 – 2666) feet.(2) Second student gets an 100 board and spends a short time calculating 100 – 33 = 67. Then thinks for a long time during which I’m sure he is going to say 67 + 1 = 68, but never quite does it. I stay silent until he announces: 667. No clue where the extra 600 came from. He wasn’t willing to write down or draw anything to explain his thinking.
Interesting! I’m inclined to put the first student in the “extending the thinking you’d do in one model to a less familiar situation” category and the second student in the associational mistake (same link) category.
One reply on “Bedtime Math Mistakes”
Wouldn’t the correct answer be ‘none’ since the boomerang would end up back at the thrower. Then again, are we counting the feet distance from the thrower or the total distance traveled? I’m pretty sure those boomerangs go in a circle or oval, not in a straight line, so the total distance travelled would be pi*diameter? yet the question asks how much farther from the thrower, but it’s not asking distance, it’s asking travel… so you’d take that circumference of a circle and half it.