It started innocently enough, with the $200 answer being: "1 + 2 + 3 + 4 + 5". Quick mental math gave the question, "What is 15?" A simple exercise in triangle numbers, which are formed by summing consecutive numbers. It's one of those things which most kids will see and do even before they hear the phrase "triangle numbers", and long before they know they memorize the formula. Besides, a small sequence like this is quicker to add (if you don't have it already memorized) than computing a formula.
Things got trickier with the $400 answer, "1 - 2 + 3 - 4 + 5". There was some hesitation as the contestants (I almost typed "students") worked that one out before one of them arrived at "What is 3?" (I didn't tape it, so I can't review it to see if someone got it incorrect first. I don't remember.) There are two short cuts for this problem, and both have to do with pairing. If you noticed that each pair "1 - 2" and "3 - 4" yield a result of "-1", you have -1 + -1 + 5, which is 3. If you noticed that "-2 + 3" and "-4 + 5" yield a result of "+1", then you had 1 + 1 + 1, which is still 3. If you just oscillated your numbers, you took more time and you probably didn't buzz in in time.
The kids gave up on the third answer: "1 * 2 * 3 * 4 * 5". Given the ages of the kids, I would have thought that at least one of them had seen factorial before, and this was the definition of 5!, although the numeric equivalent was needed. Perhaps they got stuck on 24 * 5, not thinking to reverse the order (20, 60, 120, 120). Whatever the reason, no one got the answer, and they bailed on the category.
It proved so unpopular that when Trebek cautioned "less than a minute to go" (a.k.a < 1 min), the two Math clues remained, and were the final ones of the game.
The $800 answer: "-1 * 2 * -3 * 4 * -5". This actually bothered me that none of the kids gt it. First, for the reason Alex gave. Second, because I had to listen to Alex give it. The previous clue had a result of 120. The numbers multiplied are the same, only some of the signs have changed. Multiply a negative times a negative times a negative and the product will be negative (times two more positives, which won't affect it). The question should have been "What is -120?", which should have been easy considering the previous question gave them the number, and they only had to add on the sign.
The final reason to be annoyed? Alex took so long to explain what should have been obvious that we didn't get to see the last clue. Would it have had division? Exponentiation? Mathematical minds want to know!
But that clue won't be revealed, and it's likely that they avoid such mathematical categories during future Kids Weeks.
UPDATE: I wrote a little More about that Jeopardy category after the blog The Political Hat referenced this entry.
And Jeopardy had Another Math category, with adults, shortly after this.
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