when a certain tree was first planted, it was 4 feet tall,and the height of the tree increased by a constant amount each year for the next 6 years. At the end of the 6th year,the tree was 1/5 taller than it was at the end of the 4th year.By how many feet did the height of the tree each year. a 3/10 b 2/5 c 1/2 d 2/3 e 6/5 读完题感觉挺简单的啊，可是怎么都算不出来结果，最近做题做的太多，都晕了，望NN给予指点。
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发表于 2010-11-8 11:13:41
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