3道数学题大家讨论讨论

Bourne_NY

    

(1).
15 homes sold in town, average (arithmetic mean) sale price was
150,000 and median price was 130,000. which of the following must be
true?

    

1. at
       least one of the homes was sold for more than 165,000;

   
           

2. at
       least one of the homes was sold for more than 130,000 and less than
       150,000;

   
           

3. at
       least one of the homes was sold for less than 130,000.

   
           

    

(2).
A law firm consists of 4 senior partners and 6 junior partners. How
many different groups of 3 partners can be formed in which at least
one member of the group is senior? (two groups are considered
different if at least one group member is different.)

    

    

    

(3).
If x and y are positive integers, is the product xy even?

    

5x-4y
is even;

    

6x+7y
is even;

——都做错了，而且不知道正确解题思路应该是啥样的。

novanicki

1.i 150,000-130,000=20,000说明肯定有个数是大于等于170,000的.所以I对

中位数是130,000可能另外7个数都是130,000所以II不对同理III不对.

2. c41c62+c42c61+c43=100

也可以c103-c63=100

3.d

条件1:x是偶数所以xy是偶数

条件2:y是偶数所以xy是偶数

jikuren

这几题我也有点晕，NOVANICKI解释得很到位，大谢！

Bourne_NY

谢谢了！

maimai2009

这几题是JJ题目？

Bourne_NY

不是，是GMATPrep里的。