[讨论]jj13

jackco

13. DS 两个数集, 一个含P 个10, 一个含Q 个20. 问总共的算数平均数?
(1) P+Q=100 (2) P > 50
[讨论]原作者选 C

I think the answer is A, if C were correct, A were correct by the clue of original author, right? the key factor is that you need to know P=? and Q=? because p+Q=100, therefore p=1, q=99; p=2,q=98 and so on. you always can get the mean, so the data is suficient.

猫猫头

这道题目有问题吧？
A肯定不对
倒底是问平均数还是中数？

jackco

if it is median, the answer will be c. right? because the 5oth is 10 and the 51th is 10, so the median is 10.

猫猫头

可是原JJ好象问的是算数平均数哎

jackco

if it is, which answer is correct? A or C ?

猫猫头

其实我真的觉得这道题目有问题
不是问题问错了
就是题目错了
可能（1）、（2）里面的P、Q指的都是两个集合的总数而非个数
我觉得哦

philixlau

这种题目部可能是问mean,依照ets的出题风格应该是median

lisaislisa

this pro is somewhat similar with the one I posed here
x< y
( x/(x+y))*10 + ( y/(x+y) )*20 = k
R：式子=(10x+20y)/(x+y)=10+10/(x/y+1)=k,
AS Y/（2Y）< Y/（X+Y < Y/Y
THAT IS， 1/2 < Y/（X+Y) < 1
SO， 15< k< 20， 取18。

and if we assume the pro is identical from its original one , the answer is E as far as I can see .....^^

tongxun

答案是E。
（10P +20Q）/30
P=1，Q=99，1990/30
P=2，Q=98，1980/30
因此，条件1）不充分
条件2）单独肯定不充分。
条件1）+条件2）：
P=51，Q=49； 1490/30
P=52，Q=48；1480/30
因此也不充分。
选E