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根据已知条件与未知条件相等的关系,把未知条件转化为已知条件,使隐蔽的数量关系明朗化,最后使问题迎刃而解,这就是代换的数学思想方法。一、直接代换例1 9千克荔枝和2千克桂圆共168元,已知5千克荔枝的价钱等于2千克桂圆的价钱,求荔枝和桂圆单价各是多少元?分析与解根据题意,直接代换,9千克荔枝钱数和5千克荔枝钱数是168元,每千克荔枝单价168÷(9+5)=12(元),每千克桂圆单价12×5÷2=60(元)。二、转化代换
According to the relationship between the known conditions and the unknown conditions, the unknown conditions are transformed into the known conditions so as to clarify the relationship between hidden numbers. Finally, the problem is solved, which is the mathematical method of substitution. First, the direct substitution Example 1 9 kg lychee and 2 kg longan a total of 168 yuan, 5 kg lychee is known to be equal to the price of 2 kg longan, how many lychees and longan unit price? Analysis and solution according to the motto, direct Substitution, 9 kg litchi money and 5 kg litchi money is 168 yuan, 168 yuan per kilogram of lychee price (9 +5) = 12 (yuan), each kilogram of longan unit price 12 × 5 ÷ 2 = 60 (million). Second, conversion substitution