数学T paper 2讨论专区

Lov瑜瑜4ever

带角度进去check就知道哪里错了咯。。。

ultikiller

带角度进去check就知道哪里错了咯。。。
Lov瑜瑜4ever 发表于 11-10-2010 11:54 PM

怎么做？请指教。

ultikiller

有两个可能:
1)我做错


2)题目错
Allmaths 发表于 11-10-2010 11:13 PM

我打错题目。Given that sin (x+y) = p cos(x-y), show that tan x = p - tan y/1 - p tan y。

數學神童

A student committee comprising of 8 people is to be selected from a group of 10 boys and 4 girls. In how many ways can this be done if the committee comprises of at least 3 boys and 3 girls?
After a round of interview was conducted by the selection team, the student committee of 5 boys and 3 girls was finally formed. The student committee holds regular meetings in a discussion room where they are seated at a round table with 8 seats.
Find the number of ways they can be seated if
a. there is no restriction,
b. no two girls are to sit next to each other.
At a particular meeting, two boys in the committee are absent. Find the number of ways the other members of the committee can be seated if the meeting is still held in the same discussion room with the same round table with 8 seats.

peaceboy

A student committee comprising of 8 people is to be selected from a group of 10 boys and 4 girls. In ...
數學神童 发表于 13-10-2010 02:21 PM

A student committee comprising of 8 people is to be selected from agroup of 10 boys and 4 girls. In how many ways can this be done if thecommittee comprises of at least 3 boys and 3 girls?
    (10C5 * 4C3) + (10C4 * 4C4)=1218

After a round of interview was conducted by the selection team, thestudent committee of 5 boys and 3 girls was finally formed. The studentcommittee holds regular meetings in a discussion room where they areseated at a round table with 8 seats.
Find the number of ways they can be seated if
a. there is no restriction,
(8-1)! = 7!=5040

b. no two girls are to sit next to each other.

(5!*5*4*3)/8=900 <<<很不确定的说....懒惰一个一个try = =

At a particular meeting, two boys in the committee are absent. Find thenumber of ways the other members of the committee can be seated if themeeting is still held in the same discussion room with the same roundtable with 8 seats.

6! +[6!*6C2+6!*6]/8  =2610

超高难度，答案是什么？

Lov瑜瑜4ever

b. no two girls are to sit next to each other.
if 2 girls sit next to each other,
3C2x2!x(7-1)!=4320
if 3 girls sit together,
3C3x3!x(6-1)!=360
so, 5040-4320-360=360#

At a particular meeting, two boys in the committee are absent. Find thenumber of ways the other members of the committee can be seated if themeeting is still held in the same discussion room with the same roundtable with 8 seats.

8P6=20160

我也不懂我的答案对不对得。。。
这题的确有点难度。。。

數學神童

this is the question from sarawak trial 2009 and i don have the marking scheme so i don know the answer sorry

peaceboy

this is the question from sarawak trial 2009 and i don have the marking scheme so i don know the ans ...
數學神童 发表于 13-10-2010 08:22 PM

    不会吧，sarawak出这么难的.....

peaceboy

this is the question from sarawak trial 2009 and i don have the marking scheme so i don know the ans ...
數學神童 发表于 13-10-2010 08:22 PM

    我又做多了一次，这次比较准　


After a round of interview was conducted by the selection team,thestudent committee of 5 boys and 3 girls was finally formed. Thestudentcommittee holds regular meetings in a discussion room where theyareseated at a round table with 8 seats.
Find the number of ways they can be seated if
a. there is no restriction,
(8-1)! = 7!=5040

b. no two girls are to sit next to each other.

method 1
(5!*5*4*3)/５=１４４０

method 2
If 3 girls sit together,
3!x(6-1)!=720

If 2 girls sit together,
3C2x2!x 5C2 x 2! x (5-1)!=2880
5C2 x 2! to make sure both the side of the girls is boy

5040-2880-720 = 1440


At a particular meeting, two boys in the committee are absent. Findthenumber of ways the other members of the committee can be seated ifthemeeting is still held in the same discussion room with the sameroundtable with 8 seats.

method 1
6! + (6!x6x5)/(6x2) = 2520

method 2
(8-1)!/2! =2520

Lov瑜瑜4ever

赞同楼上的所有答案。。。

數學神童

mind to explain the last 2 methods??

Lov瑜瑜4ever

mind to explain the last 2 methods??
數學神童 发表于 14-10-2010 09:04 PM

如果是我的做法啦

b. no two girls are to sit next to each other.

with no restriction=(8-1)!=5040

If 3 girls sit together,
3C3x3!x5!=720

If 2 girls sit together,
3C2x2!x4x5!=2880
3个女生，2个坐在一起，还剩1个女生和6个空位，但是剩下的女生不能坐在另外2个女生的旁边，所以剩下的那个女生只能坐4个空位(所以就x4)，之后就剩下5个空位，让5个男生进去坐(5!)

5040-2880-720=1440

At a particular meeting, two boys in the committee are absent. Find the number of ways the other members of the committee can be seated if the meeting is still held in the same discussion room with the same round table with 8 seats.

2个男生没来
所以就只有3个男生，3个女生和2个空位
所以就是(8-1)!/2!=2520
因为那2个空位是identical的
所以要divide by 2!

long_sign

sorry! 可以教导一下......
If X~ N(240,64) find
a)m such that p(l X-240 l <m)=0.80
B)r such that P( l X-240 l >r) = 0.08

peaceboy

回复 454# long_sign


    a)m such that p(l X-240 l <m)=0.80

p(l X-240 l <m)=0.80
p(-m< X-240  <m)=0.80
1-2P(x-240 > m) =0.8
2P(x-240 > m) =0.2
P(x-240 > m) =0.1
P(z>m/8) =0.1

然后自己来


B)r such that P( l X-240 l >r) = 0.08

P(x-240 > r) + P(x-240 < -r) = 0.08
2P(x-240 > r)=0.08
P(x-240 > r)=0.04
P(z > r/8)=0.04

然后自己来

數學神童

the lifespan,in hundred hours, of an electrical devise is a random variable T with the probability density function
f(t)=  (1/50)e^(-t/50)     for t=>0
           0                                otherwise

find the probability that the devise will function after 600 hours

數學神童

Given that there are 5 girls and 3 boys.A committee which consists of 3 members is formed.Find the number ways that can be done where
a)the committee must have 2 boys
b)the committee has more boys than girls

peaceboy

回复 456# 數學神童


    1-f(0)-f(1)-f(2)-f(3)-f(4)-f(5) -f(6) = 1- 0.02 - 0.0197 - 0.0192 - 0.0188- 0.0185 - 0.0181 -0.0177
                                                   =0.868

随便做

peaceboy

回复 457# 數學神童


    Given that there are 5 girls and 3 boys.A committee which consists of 3members is formed.Find the number ways that can be done where
a)the committee must have 2 boys

3C2 * 5C1 = 15


b)the committee has more boys than girls

3C2*5C1 + 3C3*5C0 = 15+1
                             =16

Lov瑜瑜4ever

回复  數學神童


    1-f(0)-f(1)-f(2)-f(3)-f(4)-f(5) -f(6) = 1- 0.02 - 0.0197 - 0.0192 - 0.0188- ...
peaceboy 发表于 20-10-2010 04:46 PM

这个是normal distribution那课的？

peaceboy

回复 460# Lov瑜瑜4ever


    其实我不会的，没错的话好像是要用integration的，math T的syllabus

1- integrate (1/50)e^(-t/50) , t from 0 to 6 <<<我其实觉得这个比较像答案