[求助]一道PREP上的数学

MangoQQ

 In a certain deck of cards, each card has a positive integer written on it, In a multiplication game, a child draws a card and multiplies the integer on the card by the next larger integer.  If each possible product is between 15 and 200, then the least and greatest integers on the cards could be:

a. 3 and 15

b. 3 and 20

c. 4 and 13

d. 4 and 14

e. 5 and 14

答案: C.

为啥我做出来是4 和12呢. 请各位指教.

MangoQQ

再加一道,

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 tree increase each year?

a. 3/10    

b. 2/5

c. 1/2

d. 2/3

e. 6/5

answer: d

为啥我老是算出来是2/5?

MangoQQ

没人帮我吗?  自己顶一下.

gonghao

以下是引用MangoQQ在2007-5-23 6:05:00的发言：

 In a certain deck of cards, each card has a positive integer written on it, In a multiplication game, a child draws a card and multiplies the integer on the card by the next larger integer.  If each possible product is between 15 and 200, then the least and greatest integers on the cards could be:

a. 3 and 15

b. 3 and 20

c. 4 and 13

d. 4 and 14

e. 5 and 14

答案: C.

为啥我做出来是4 和12呢. 请各位指教.

这题好怪，我算出来是D

最小值只能是最小的两个数相乘所得，3*4=12落在范围外，4*5=20落在范围内（最小4）

最大值只能是最大的两个数相乘所得，13*14=182应该也小于200啊，14*15=210大于200（最大14）

所以我得出是D，大家讨论是否有错误

gonghao

以下是引用MangoQQ在2007-5-23 6:30:00的发言：

再加一道,

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 tree increase each year?

a. 3/10    

b. 2/5

c. 1/2

d. 2/3

e. 6/5

answer: d

为啥我老是算出来是2/5?

[(4+6x)-(4+4X)]/(4+4X)=1/5X

X=2/3

strout

13*(13+1) = 184.

13 is the max number. The question is asking for the original number without adding 1.

For the second question:

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

h = 2/3

MangoQQ

多谢各位啦, 明白了. 不好意思, 这么简单的问题都不会.

MangoQQ

13*(13+1) = 184.

13 is the max number. The question is asking for the original number without adding 1.

For the second question:

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

h = 2/3

马上就要考试了吧, 祝你交运啊,考个牛! 到时候多送点好吃的"鸡精"给我们呀.

MangoQQ

发贴好象有问题啊, 怎么发出来漏字啦?