一道prep数学求解

ozymendias

36.   
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
这题答案选C，我怎么觉得选D呢。 14*13<200呀

ozymendias

还有这个
177.        18457-!-item-!-187;#058&011601
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?

(A)  3/10
(B)  2/5
(C)  1/2
(D)  2/3
(E)  6/5
我知道这题很简单，但我总算不对。我的思路是 4+6x-(4+4x)=1/5, 这样算出来是1/10. 我到底怎么错了呀

avalon9527

第一题，如果有14，那么当他抽中14时应该是14*15=210，这样就不符合题意了。所以应该是13.
第二题，[(4+6x)-(4+4x)]/(4+4x)=1/5                          x=2/3. 它说1/5 taller并不是1/5 feet taller.
gmat数学都不难，但千万要细心。

s

回复 2# ozymendias


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xiexiang

第一题后面应该是14*15，不是14*13

xiexiang

第二题1/5是百分比的关系，第六年的高度是第四年的1.2倍

daoyinger

第一题就是13*14<200才是between200吖~D里的14*15是大于200 就不在15到200的范围里了，故C
第二题你理解错了 高1/5是比值，应该是（4+4x）*（1+1/5）=4+6x  ==>x=2/3

ozymendias

恩，谢谢大家