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official guide (OG) 11th edition 215 [#permalink]
 16 Apr 2009, 08:35
Question Stats:
33% (00:00) correct
66% (00:51) wrong based on 0 sessions
if m is the average (arithmetic mean) of the first 10 positive multiples of 5 and if M is the median of the first 10 positive multiples of 5, what is the value of M-m?
a. -5
b. 0
c. 5
d. 25
e. 27.5
according to the answer in OG, the first 10 positive multiples are 1,2,3, ...,8,9,10, but i think positive number could also be 1.1, 1.2 .... or some other number which bigger than 0.
the correct answer is e, but why? Thks a lot
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Re: official guide (OG) 11th edition 215 [#permalink]
16 Apr 2009, 09:22
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"MULTIPLE" by definition has to be resulted when multiplied by a an Integer. For example, 10 is a multiple of 5 because when 5 is multiplied by 2, it results in 10. In the same way, 5 x 1.5 = 7.5 doesn't imply that 7.5 is a multiple of 5 because 1.5 is not an integer. The answer, First 10 positive multiples of 5 are = 5,10,15,20,25,30,35,40,45,50. Arithmetic mean would be = 5(1+2+3......9+10)/10 = 27.5 In the same way, Median = (25+30)/2 = 27.5 Thus, M-m = 0. Official Answer as listed in OG 11 is B.
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Re: official guide (OG) 11th edition 215 [#permalink]
20 Apr 2009, 07:57
Goldenagle94,
catch your point.
thks a lot:)
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Re: official guide (OG) 11th edition 215 [#permalink]
20 Apr 2009, 09:42
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Here one important rule to remember is that, for equally spaced numbers median=mean. Therefore, mean-median=0. we dont need to solve it.
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Re: official guide (OG) 11th edition 215 [#permalink]
21 Apr 2009, 07:17
bandit wrote: Here one important rule to remember is that, for equally spaced numbers median=mean. Therefore, mean-median=0. we dont need to solve it. thks. 
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Re: official guide (OG) 11th edition 215 [#permalink]
21 Apr 2009, 07:45
bandit wrote: Here one important rule to remember is that, for equally spaced numbers median=mean. Therefore, mean-median=0. we dont need to solve it. what does "equally spaced" mean?
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Re: official guide (OG) 11th edition 215 [#permalink]
22 Apr 2009, 00:52
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kbulse wrote: bandit wrote: Here one important rule to remember is that, for equally spaced numbers median=mean. Therefore, mean-median=0. we dont need to solve it. what does "equally spaced" mean? For numbers in arithmatic progression (AP). For example 1,2,3,4,5,6 5,10,15,20,25 3,6,9,12
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Re: official guide (OG) 11th edition 215 [#permalink]
23 Apr 2009, 14:40
smart tip by goldeneagle and bandit
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Re: official guide (OG) 11th edition 215
[#permalink]
23 Apr 2009, 14:40
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