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一、问题的提出[例1]有8只乒乓球外形相同,其中有一只质量稍轻的次品,给你一架不带砝码的天平,问最少用天平测几次定可找出次品?解决该问题一般采用“穷举法”,即把各种可找出次品的方法都找出来,通过比较得出测量次数最少的方法.“穷举法”很繁琐,例1找次品的方法就有三种.方法一:8只球中任选两球分放天平两盘中称.这样测四次定可找出次品.方法二:8只球按4只一组分为两组,分放天平两盘
First, the question is presented [Example 1] There are eight table tennis balls with the same appearance. One of them has a slightly lighter quality, giving you a balance without a weight, and asking you to use a balance at least for several times to find out the times. Products to solve this problem generally use the “exhaustion method”, that is, to find out all kinds of methods can find out the inferior, by comparing the method to obtain the least number of measurements. “Exhaustive method” is very tedious, Example 1 find times There are three methods for the product. Method One: Choose two balls in 8 balls and place them in two plates in the balance. This test can be used to find defective products four times. Method two: Eight balls are divided into groups of four. Two groups, divided two balances