有些数学问题,从条件出发顺向思考很难找到答案,那么不妨倒过来想一想,再加上表格的帮助,就显得容易多了。例1李大妈卖西瓜,第一次卖出去全部的一半少1个;第二次卖出去剩下的一半多1个;第三次卖出剩下的一半多2个,这时李大妈还有4个瓜没卖。她原来共有多少个西瓜?分析:由“第三次卖出剩下的一半多2个,这时李大妈还有4个西瓜没卖”可知,李大妈1 Some mathematical problems, starting from the conditions forward thinking difficult to find the answer, then may wish to think about it, coupled with the form of help, it is much easier. Example 1 Aunt Lee sold watermelon, the first sold less than one half of all; the second sold more than half of the remaining one; the third sold more than half of the remaining two, then Lee Aunt there are four melons did not sell. Her original total number of watermelon? Analysis: from the third sold more than half of the remaining two, then Aunt Lee did not sell four watermelon ", Aunt Lee 1