余数，概率等求助大家！！

winny莹 · 发表于 2011-2-23 14:38:02

The figure above shows the dimensions of a semicircular cross section of a one-way tunnel.The single traffic lane is 12 feet wide and is equidistant from the sides of the tunnel.If vehicles must clear the top of the tunnel by at least ½ foot when they are inside the traffic lane, what should be the limit on the height of vehicles that are allowed to use the tunnel? 答案是7.5 为什么不是9.5？不是半径10减去0.5嘛？

Q25:
A certain roller coaster has 3 cars, and a passenger is equally likely to ride in any 1 of the 3 cars each time that passenger rides the roller coaster.If a certain passenger is to ride the roller coaster 3 times, what is the probability that the passenger will ride in each of the 3 cars?
答案二分之九

Q26:
There are 8 books on a shelf, of which 2 are paperbacks and 6 are hardbacks.How many possible selections of 4 books from this self include at least one paperback?
答案：55

GWD2

Q2:头疼的余数

When positive integer x is divided by positive integer y, the remainder is 9.If x/y = 96.12, what is the value of y? 答案：75

The figure above shows the dimensions of a semicircular cross section of a one-way tunnel.The single traffic lane is 12 feet wide and is equidistant from the sides of the tunnel.If vehicles must clear the top of the tunnel by at least ½ foot when they are inside the traffic lane, what should be the limit on the height of vehicles that are allowed to use the tunnel? 答案是7.5 为什么不是9.5？不是半径10减去0.5嘛？

Q25:
A certain roller coaster has 3 cars, and a passenger is equally likely to ride in any 1 of the 3 cars each time that passenger rides the roller coaster.If a certain passenger is to ride the roller coaster 3 times, what is the probability that the passenger will ride in each of the 3 cars?
答案二分之九

Q26:
There are 8 books on a shelf, of which 2 are paperbacks and 6 are hardbacks.How many possible selections of 4 books from this self include at least one paperback?
答案：55

GWD2

Q2:头疼的余数

When positive integer x is divided by positive integer y, the remainder is 9.If x/y = 96.12, what is the value of y? 答案：75

Gail小M · 发表于 2011-2-23 17:17:31

Q25 3*2*1/3*3*3=6/27=2/9
Q26 C4 8(上面是4，下面是8)--C(4 6)=70-15=55
GWD2 the remainder 9=0.12 y, y=75
还有一题图看不到就没看题目~

winny莹 · 发表于 2011-2-23 19:12:37

第二十五还是有疑惑野，1/3乘以1/3乘以1/3应该指的是每个车被选中的概率吧，前面3乘以2是什么意思啊？
真是惭愧，数学一向不好，有劳大侠费心指点！！

Q25 3*2*1/3*3*3=6/27=2/9
Q26 C4 8(上面是4，下面是8)--C(4 6)=70-15=55
GWD2 the remainder 9=0.12 y, y=75
还有一题图看不到就没看题目~

-- by 会员 Gail小M (2011/2/23 17:17:31)

winny莹 · 发表于 2011-2-23 19:17:37

最后一题的图很让我崩溃，怎么都贴不上来！！
其实，就是一个半圆型，直径标的是20米宽，象征一个山洞公路的截面。题目说这个洞洞有条单行路是12米宽，还说通过山洞的车辆必须与洞顶留有至少0.5米的空隙，（应该是真么翻译吧）问穿过山洞的车有多高才行？

Gail小M · 发表于 2011-2-23 19:23:04

是(3* 2 *1) /(3*3*3) 3cars, first 3choices, after U have picked one, there are 2cars, thus U have 2 choice, in the end, one choice.

winny莹 · 发表于 2011-2-23 19:29:55

懂了==!

sdcar2010 · 发表于 2011-2-23 21:54:24

There are 8 books on a shelf, of which 2 are paperbacks and 6 are hardbacks.How many possible selections of 4 books from this self include at least one paperback?
答案：55

To get at least 1 paperback:

1 paperback only: 2*[6*5*4/3*2*1] = 40
2 paperback only: 1*[6*5/2*1] = 15

Total = 55

sdcar2010 · 发表于 2011-2-23 21:56:42

When positive integer x is divided by positive integer y, the remainder is 9.If x/y = 96.12, what is the value of y? 答案：75

x = y*k + 9; x/y = k + 9/y = 96.12

So k = 96 and 9/y = 0.12. so y = 75

sdcar2010 · 发表于 2011-2-23 22:03:42

最后一题的图很让我崩溃，怎么都贴不上来！！
其实，就是一个半圆型，直径标的是20米宽，象征一个山洞公路的截面。题目说这个洞洞有条单行路是12米宽，还说通过山洞的车辆必须与洞顶留有至少0.5米的空隙，（应该是真么翻译吧）问穿过山洞的车有多高才行？

-- by 会员 winny莹 (2011/2/23 19:17:37)

Hehe. The car is not a single slim LINE, but a 12 feet wide block. What the question wants you to do is to draw a right angle triangle: whose horizontal side is 6, vertical side is (height + 0.5) and the longest side is 10. 6^2 +(height +0.5)^2 = 10^2

height = 7.5

kazemi · 发表于 2011-2-23 23:12:51

看不到图啊，mm

不过已经有人替你解啦，+U~

余数，概率等求助大家！！

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