yinyanwu0188

HELP!!!!!!!!!!! Different idea! 7. 某筐里有十个苹果，两个烂了，问拿两个都是好苹果的概率？ [确认]：28/56 [思路]: c(2,8)/c(2,10)=28/56 I think the answer should be 8/10 *7/9 =56/90 9. 7根绳子，MEAN=68，MEDIAN=84，最长的是最短的的四倍再加14，问最长的长度范围，这题我当时没有算出来，乱选了一个，记得有一个选项是BETWEEN 82 AND 152。 [确认]： [思路]:因为median=84,所以最长的绳子一定>=84,所以最长绳子的下限是84；最短的绳子一定<68,大于17.5,===>最长的绳子上限是68*4+14=286. The above mathod does not takce account the MEAN IS 68. I think the longest one should be 171.5. ------ 17.5*3+84*3+longest=68*7

yinyanwu0188

Sorry , the answer for question 9 should be the following one. What do you think? 9. 7根绳子，MEAN=68，MEDIAN=84，最长的是最短的的四倍再加14，问最长的长度范围，这题我当时没有算出来，乱选了一个，记得有一个选项是BETWEEN 82 AND 152。 [确认]： [思路]:因为median=84,所以最长的绳子一定>=84,所以最长绳子的下限是84；最短的绳子一定<68,大于17.5,===>最长的绳子上限是68*4+14=286. The above mathod does not takce account the MEAN IS 68. I think when the first three ropes are all the shortest and the 4th,5th,6th is median(84).at this time we can get the longest one, which should be 132. [(X-14)/4]*3+84*3+X=68*7 THEN X=132

yinyanwu0188

The longest one must be longer than 84, so the answer should be 84-134