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求助一道数学题

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楼主
发表于 2008-5-1 13:35:00 | 只看该作者

求助一道数学题

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 increase each year?

answer: 2/3

why

沙发
发表于 2008-5-1 15:50:00 | 只看该作者

設constant amount increased each year=a

first planted=4

end of first year=4+a

end of second year=4+2a

...由此类推

end of 4th year=4+4a

end of 6th year=4+6a

(4+6a)= (6/5)*(4+4a)

可以算出 a=2/3

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