问题 解答题

已知甲盒内有大小相同的2个红球和2个黑球,乙盒内有大小相同的3个红球和3个黑球.现从甲、乙两个盒内各任取2个球.

(Ⅰ)求取出的4个球均为红球的概率;

(Ⅱ)求取出的4个球中恰有1个红球的概率.

答案

(I)取出的4个球均为红球的取法为C22×C32=3,所有的取法C42×C62=90,故所求的概率是

3
90
=
1
30

(II)取出的4个球中恰有1个红球包含的基本事件是C31×C31+C21×C21×C32=21

故所求的概率是

21
90
=
7
30

阅读理解

阅读理解。

     When you learn reading, math, and other subjects taught in school from your parents or tutors (家庭教师)

who come to your house, it's called homeschooling. A kid may be the only one, or he or she may be taught

with brothers, sisters, or kids from the neighborhood.

     Parents choose to homeschool their children for many different reasons.   1   But more often, kids are

homeschooled because their parents feel they can give their child a better education than the local school

can.   2   

     If you don't like school, homeschooling might seem like the perfect solution. But it's better for everyone

if homeschooling isn't chosen just as an escape from school or problems there, such as bullying.   3   Your

school counselor (顾问) and other school officials, such as the principal, often can help. 

      4    It's true that kids must be educated, but it's legal to be schooled at home in the US. In fact, more than

1 million students do it. These kids can learn just as they do in regular schools, but their parents are in charge

of their education. 

       5   The parents also may have to file paperwork with the state to explain who's teaching the kid and

which subjects are being covered.

A. Homeschooling is very popular in the United States.

B. Sometimes a kid is sick and can't go to regular school.

C. Finding solutions to the problem should be the first step.

D. Some people's kids should attend public schools.

E. Homeschool parents must make sure that their kids get the instruction and the experiences they need.

F. You might wonder if kids have to go to school.

G. Parents also may choose homeschooling because they want their child's education to include religious

  instruction, which isn't offered at public schools.

问答题