兒女都不是天才，但老爸還是可以進步的 by A-mao

兒子昨天帶回來一張數學作業，老爸一看，就知道是為州裏每年一度的統考準備的。十道題，全是一個模式：X隻昆蟲加蜘蛛，Y條腿，多少隻昆蟲，多少隻蜘蛛？

老爸問兒子：“Did your teacher show you how to do this?”

兒子回答：“No, dad. We ran out of time in the class. I guessed some of them.”

老爸一看，就知道兒子是瞎猜的。也難怪兒子，當年姐姐這個年紀從州裏統考回來，就是這道題不會解，回來問老爸呢。

老爸其實也不知道如何講解才能讓三年級孩子理解。當年給姐姐講解，是用列表的辦法。５隻昆蟲和蜘蛛，共有３２條腿，老爸想了半個小時，就教女兒列一個table: 0隻昆蟲，５隻蜘蛛，４０條腿；１隻昆蟲，４隻蜘蛛，３８條腿；。。。女兒當年是懂了。９年後，老爸又麵對同樣的問題，還是同一種解法嘛？兒子的十道題，最高的數字是１２隻昆蟲加蜘蛛，不行啊！

邊作晚飯邊想辦法。半個小時，菜飯上桌，老爸終於有了解法，可就不知道兒子是不是能理解了。

“See, this one, 8 spiders plus insects, 60 legs. We assume all are insects. 8 insect, there are 48 legs. 60-48=12. So we are 12 legs less than the 60 legs. Each time we switch one insect to a spider, we increase 2 more legs. so, we need to switch 6 insects to spiders to get 12 legs more. so it should be 6 spiders and 2 insects.“ 老爸看著兒子，希望兒子能開竅，比女兒聰敏些。

“I don't get it, dad.”兒子看著老爸發楞呢。

“Ok, you do it with a pencil and paper. 8 insects plus spiders. Assume all 8 animals are insects, how many legs?”老爸死心了，知道兒子不是天才。

“6,12, 18, 24....48 legs!”兒子扳指頭作乘法還是挺在行的。

“Great! So 48 legs, it is 12 less than the 60 legs, right?”老爸耐心地問。

“Yes.”

“Then, we have to increase spider number to get more legs. When you change one insect to a spider, we get 2 more legs. so for 12 more legs, how many spiders you need?”

“That's easy, 6 more spiders.”兒子回答。

“Then, it is 6 spiders, and 2 insects. Let's see whether the anser is right. 6 spiders, 48 legs, and 2 insects, 12 legs. So the total legs are 60, matching the answer. Correct!”

“Oh, I get it! Let me finish the rest.” 兒子邊吃邊解題，十幾分鍾都解出來了。

 

嘿嗨，老爸沒有天才基因，兒女如何能成天才？不過，笨老爸還是可以慢慢改進自己的教育方法的。

（老爸今天想引進代數的概念(X)，兒子是“I don;t know what you are talking about, dad!”。老爸徹底死心了。）

（１０／２２／２００８）
---編者話外音:為有耐心有智慧的父母致敬!