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Witnesses to a meteor in Australia in 1978 claimed to have heard strange noises as it streaked overhead. Yet, given that the meteor was 30 kilometers up, if these sounds had come directly from the meteor, people on the ground could not have heard them until almost a minute after the meteor had disappeared. Physicist Colin Keay hypothesized that the light given off by a meteor's trail must be accompanied by invisible electromagnetic radiation in the form of very low frequency (VLF) radio waves. Such waves, which travel at the speed of light, would reach the observer when the meteor itself came into view.
Subsequent experiments in a soundproof chamber showed that many things can act as transducers to convert VLF waves into audible vibrations. Aluminum foil, thin wires, pine needles, or dry hair all responded to a VLF field. VLF waves induce small charges in such objects, thereby causing them to vibrate in time with the waves' oscillation. This transducer effect would explain why some people heard the noises while others close by heard nothing. Those who heard sounds were simply nearer to transducers. It could also explain why attempts to record meteor sounds have failed: scientists carefully place their microphones away from possible sources of interference.
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[数学 ]【新版】冲分救命题 -12222
Three numbers are to be selected at random and without replacement from the five numbers 4, 5,7,8, and 11.What is the probability that the three numbers selected could be the lengths of the sides of a triangle?
[数学 ]【新版】冲分救命题 -12221
There are 5!. or 120. ways of arranging 5 different solid-colored flags side by side. If the colors of the flags are red, blue，yellow，green, and orange，how many of those arrangements have either the red fag or the blue flag in the middle position?
[数学 ]【新版】冲分救命题 -12220
k is randomly selected from the set of integers from 1 to 100, inclusive.
[数学 ]【新版】冲分救命题 -12219
REENA'S MOVIE COLLECTION The table above shows the number of movies in each genre in Reena's movie collection. If two different movies are to be selected at random from the collection. what is the probability that neither movie will be in the science fiction genre?
[数学 ]【新版】冲分救命题 -12218
Several 0 and 1 are arranged in a 10*10 palace as follows. Among all the number 0, what is the probability that they are arranged in both an odd row and an odd column? Give your answer as a fraction.
[数学 ]【新版】冲分救命题 -12217
There are 5!, or 120,ways of arranging 5 different solid-colored flags side by side. If the colors of the flags are red, blue,yellow, green, and orange,how many of those arrangements have either the red flag or the blue flag in the middle position?
[数学 ]【新版】冲分救命题 -12216
Pat has five matched pairs of socks and no two of the pairs are the same color. If Pat selects two socks simultaneously and at random, what is the probability that the two socks selected will be a matched pair.
[数学 ]【新版】冲分救命题 -12215
A box contains 100 purple balls, 100 red balls, and 100 white balls. What is the minimum number of balls that must be chosen to ensure that at least 4 of the balls chosen have the same color.
[数学 ]【新版】冲分救命题 -12214
The cast of a certain play has 2 male characters and 2 female characters. The director of the play will select the 2 male characters from 6 male actors and the 2 female characters from 8 female actors. How many different sets of 4 actors, consisting of 2 male actors and 2 female actors, are there that can be selected by the director?
[数学 ]【新版】冲分救命题 -12213
P is the set of all of all positive factors of 20, and Q is the set of all positive factors of 12. If a member of Pwill be chosen at random, what is the probability that the chosen member will also be member of Q .
[数学 ]【新版】冲分救命题 -12212
Average Per-Pupil Expenditures for the I0 Percent of School Districts State X That Had the Highest Expenditures (Group H) Compared to the 10 Percent of School Districts That had the Lowest Expenditures (Group L)
[数学 ]【新版】冲分救命题 -12211
Average Per-Pupil Expenditures for the 10 Percent of School Districts State X That Had the Highest Expenditures (Group H) Compared to the 10 Percent of School Districts That had the Lowest Expenditures (Group L)For the 1986-87 school year, the ratio of the average per-pupil expenditures or the Group L districts to the average for the Group H districts was closest to
[数学 ]【新版】冲分救命题 -12210
Average Per-Pupil Expenditures for the I0 Percent of School Districts State X That Had the Highest Expenditures (Group H) Compared to the 10 Percent of School Districts That had the Lowest Expenditures (Group L) From the 1979-80 school year to the 1989-90 school year, the average per-pupil expenditures for the Group L school districts increased by approximately.
[数学 ]【新版】冲分救命题 -12209
As a telephone salesperson, Kay made an average (arithmetic mean) of x sales calls per day for n consecutive days. On the next day, she made k sales calls. Which of the following represents the average number of sales calls per day for the n+1 days?
[数学 ]【新版】冲分救命题 -12208
Set S consists of 8 positive integrs,3 of which are even, Set T consists of all numbers of the form x+x2 ,where x is member of set S.
[数学 ]【新版】冲分救命题 -12207
Lists S and T each consist of 5 consecutive integers. The greatest integer in S is equal to the least integer in T.
[数学 ]【新版】冲分救命题 -12206
[数学 ]【新版】冲分救命题 -12205
List S : 1,2 ,3, k,2k If k< 2, which of the following numbers could be the median of the five numbers in list ? Indicate all such numbers.
[数学 ]【新版】冲分救命题 -12204
In 1990 approximately what percent of the total population of neighborhood was foreign-born with Europe as region of origin?
[数学 ]【新版】冲分救命题 -12203
A list of the names of the people of the entire 1990 foreign-born population in neighborhood was generated, with each person’s name appearing once. The names of 2 different people will be randomly selected from the list. Which of the following is closest to the probability that both names selected will be names of people whose region of origin was “Other”?
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