最新数学jj讨论

(PS) there are two groups, part-time and full-time, part-time is 1/3 of the total, and part-time worked 3/5 hours of full time, ask what fractions of part-time working hours in total hours?  忘选什么了大家自己算吧挺简单的， 这题哪见过

这道题我怎么看不懂？希望大家帮助指点一下。

(PS) Five apples, two of them is bad, u randomly pick two apples each time for two times, what is the chance that u have picked at least two bad apples in two times?这题看着很饶口,记着第一次选完要放回去

我算是0.18，不知对否？

(PS) known that a&b are integers, a-b and a/b are both evens, ask which of following must be odd? 里面有b^2/2+1, 还有a^2/2－1，挣扎了半天最后选第一个了

这题两个都是奇数吧

(DS) One uses estimation to plan his trip. The estimated distance of trip is S miles, the estimated time of trip is T hours. He wants to know if his estimation of speed across the trip will be maintained with 0.5miles/hour?
1. Accuracy of estimated distance is within 10 miles
2. Accuracy of estimated time is within 2 hours
选E

不太清楚为什么选E

我的答案

1 1/5

2 1- (c23*c23+2*c23*c12*c13)/c25*c25=0.55

3 a-b even,a/b even 得出 a and b are both even 

4 12说的是误差范围，没有路程和时间具体值没法求

楼上的兄弟，第一题是咋算的？

我第二题的算法是(2C(3，2）*C(2,2）+2C(3,1)C(2,1))/C(5,2)^2=18%

1/3*3/5

我怎么觉得第一题是3/13 ？

part-time worked 3/5 hours of full time 假设Full time worked X hours, 那么part-time worked 3/5X hours,

part-time is 1/3 of the total, 那么 full time is 2/3 of the total.

所以part-time working hours is 3/5X * 1/3 , total working hours is 3/5X * 1/3 +2/3X

fractions of part-time working hours in total hours is:

(3/5X * 1/3) / (3/5X * 1/3 +2/3X)=3/13

1984 is a leap year, June 21 is Sunday, what day is June 21 in 1987? 这题是老管的吧

请问这道题怎么做啊？

哦，对。1搞错了，谢了

请问这题什么意思？没看懂。能不能解释一下。 谢谢。

9.    (PS)  有一个圆，半径已知（数字忘了），圆心是XY坐标系的圆点，已知圆上的两个点A,B，

       A在第二象限，B在第一象限。这两个点的坐标是已知的（数字忘了），圆上另一个点到A的距

       离等于AB的长度，求这个点的坐标。

       机经作者提示:我只记得答案选A

       根据条件可以得到圆的方程，再结合"圆上另一点到A的距离等于AB的长度"得到另一个方程。具体步骤 

       就是C（Xc,Yc）（那个某点）与B（Xb,Yb）关于AO（y=ax）对称，即(Yc+Yb)/2=a(Xc+Xb)/2谢谢rll1988同学提醒。

       两个方程一起求未知点坐标。