Please provide more information for a anwser
The 90th percentile corresponds to Z ≈ 1.28155.
Answer:
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against the wind, an airplane travels 3640 km in 7 hours.
with the wind, the same plane travels 6000 km in 6hrs.
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let speed of plane in still air be x mph
speed of wind be y mph.
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t=d/r
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against wind speed = x-y mph
with wond speed = x=y mph
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3640/(x-y)=7
3640 = 7x-7y
/7
520=x-y.....................1
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6000/x+y = 6
6000 = 6x+6y
/6
1000=x+y.....................2
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Add (1) & (2)
2x=1520
/2
x=760 mph speed of plane in still air
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plug value of x in 2
1000=760+y
100-760=y
240 = y
240 mph speed of wind
A)
First note that the plates can have between 4 and 6 symbols so we will need to find the number of plates with 4 symbols, 5 symbols and 6 symbols. We add these to get the total. In this part repetition of symbols is allowed. Since there are 26 + 10 =36 possible symbols we look at each position on the plate and think of how many choices there are. We multiply the number f choices using the counting principal since the choices are each independent -- one symbol does not affect another. There are 36 choices for the first symbol, 35 for the second and so on. The number of plates is:
4-symbols = (36)(36)(36)(36)=36^4
5 symbols = (36)^5
6 symbols = 36^6
So the total here is: 36^4+36^5+36^6
B) Here we do not repeat symbols so there are 36 choices for the first symbol but only 35 for the next and 34 for the one after and so on.
4-symbols = (36)(35)(34)(33)
5 symbols = (36)(35)(34)(33)(32)
6 symbols = (36)(35)(34)(33)(32)(31)
So the total here is: (36)(35)(34)(33)+(36)(35)(34)(33)(32)+(36)(35)(34)(33)(32)(31)
c)
In order for there to be a repeated symbol we have 36 choices for the first symbol, 36 for the next and so on. However, for the last symbol we have to pick from one of the ones already selected so there are 3, 4 or 5 choices respectively.
4-symbols = (36)(36)(36)(3)
5 symbols = (36)(36)(36)(36)(4)
6 symbols = (36)(36)(36)(36)(36)(5)
So the total here is: (36^3)(3)+(36^4)(4)+(36^5)(5)
D)
The probability is given by (the number of plates with at least one repeated symbol)/(the total number of plates if repetitions are allowed) = (the answer to c) / (the answer to a)
FVAD=515[((1+0.18/12)^(12*2)-1)/(0.18/12)]*(1+0.18/12)
FVAD=14967.46