请教数学题

11502 · 发表于 2010-8-7 15:40:49

1.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?

A.   0
B.   1/9
C.   2/9
D.   1/3
E.   1
2.If 1050 – 74 is written as an integer in base 10 notation, what is the sum of the digits in that integer?

A. 424
B. 433
C.   440
D.   449
E.   467

11502 · 发表于 2010-8-7 16:11:45

fly12404 · 发表于 2010-8-7 16:20:23

1)
分母: 3種選擇玩三次 = 3^3 =27
分子: 三種車都玩到順序隨便 = 3! =6
6/ 27 = 2/9

2)
題目應該是10^50吧 ?
10^50- 74
10^50次方共有51位數扣掉74
會剩下50位數(因為第一個1退到後面變成9)
也就是9999999999..........26 (48個9 後兩位為26)
48x9 + 2 +6 =440
: )

11502 · 发表于 2010-8-7 20:35:09

谢啦

请教数学题

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