巧用比例解题（Solving problems with proportion）.docVIP

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巧用比例解题（Solving problems with proportion）.doc

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巧用比例解题（Solving problems with proportion） Solving problems with proportion Case 1: a fraction of the numerator and is 100, if the molecular denominator plus 23, plus 32 new fraction is, how much is the original score? Thought introduction: the numerator and the new score is 1002332 = 155, after some minutes, indicating that the numerator is the ratio of 2:3, according to the proportion to do. Solution: 1002332 = 155 Molecule: 155 x = 62 Denominator: 155 x = 93 Original score: Example 2: there is a score, if the numerator adds 1, this score is equal to; if the denominator adds 1, this mark is equal to ask what the original score is Ideas read: molecules plus 1, into the denominator plus 1, the two cases are based on the sum of the original numerator and denominator plus 1, it can be seen that the numerator after the change is the same as the denominator, that is, and unchanged. The first case is the numerator of the ratio is 1:2, and 3, the latter is the numerator of the ratio is 1:3, and is the 4, the two and 3 copies, and 4 copies together for 12 copies, 1:2 = 4:8 1:3 = 3:9 at molecular changes 1 before and after, plus 1 is 4, with 1 is 3 copies, 1 copies of 1 is visible, the original molecule is 3, plus 1 before and after the change to see in the denominator, visible original denominator is 8, so the original score is . Answer: the original score is. Current learning and practical use: 1, a fraction of the numerator and is 60, if the molecular denominator minus 19, minus 1, the fraction is, how much is the original score? Solution: 60191 = 40 Molecule: 40 x Denominator: 40 x Original score 2, a fraction of the numerator and is 74, if the molecular denominator minus 12, plus 15 new fraction is, how much is the original score? Solution: 74-12+15=77 3, a fraction of its denominator minus 2, that is, after the reduction is equal to the original score; if the denominator plus 9, that is, to equal the future. Well = =. Solution: 4, a true score, if the numerator and the