1.When a certain tree was first planted ,it was 4 feet tall,and the height of the free 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?
a.3/10
b.2/5
c.1/2
d.2/3
e.6/5
为何选D
2.有多少个奇整数大于整数X，小于整数Y？
(1)12个偶整数大于整数X，小于整数Y
（2）24个整数大于整数X，小于整数Y
为何选B？
1 第四年树高4+4x
第六年树高4+6x
根据条件[(4+6x)-(4+4x)]/(4+4x)=1/5
解方程得2/3
2
根据第一个条件
如果X是偶数，Y是奇数
共12个奇数。
如果X是奇数，Y是奇数
共11个奇数，
条件不充分
根据第二个条件，
不论X、Y奇偶情况怎样，
都是有12个奇数。
所以答案选B
第一题的式子为何不是4+6X=1/5+4+4X
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