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# What is the average (mean) of all 5-digit numbers that can be formed

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Re: What is the average (mean) of all 5-digit numbers that can be formed [#permalink]
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Bunuel wrote:
What is the average (mean) of all 5-digit numbers that can be formed by using each of the digits 1, 3, 5, 7, 8 and exactly once?

(A) 48000
(B) 49999.5
(C) 53332.8
(D) 55555
(E) 56432.8

total terms = 5! = 120
and sum of all terms = fix one place so 4! * ( 1+3+5+7+8)*(11111) = 639996
avg 639996/120 = 53332.8
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Re: What is the average (mean) of all 5-digit numbers that can be formed [#permalink]
Archit3110 wrote:
Bunuel wrote:
What is the average (mean) of all 5-digit numbers that can be formed by using each of the digits 1, 3, 5, 7, 8 and exactly once?

(A) 48000
(B) 49999.5
(C) 53332.8
(D) 55555
(E) 56432.8

total terms = 5! = 120
and sum of all terms = fix one place so 4! * ( 1+3+5+7+8)*(11111) = 639996
avg 639996/120 = 53332.8
IMO C

Can you explain this method in detail, Archit?
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Re: What is the average (mean) of all 5-digit numbers that can be formed [#permalink]
[quote="Archit3110"][quote="AkshdeepS"][quote="Archit3110"][quote="Bunuel"]What is the average (mean) of all 5-digit numbers that can be formed by using each of the digits 1, 3, 5, 7, 8 and exactly once?

(A) 48000
(B) 49999.5
(C) 53332.8
(D) 55555
(E) 56432.8[/quote]

total terms = 5! = 120
and sum of all terms = fix one place so 4! * ( 1+3+5+7+8)*(11111) = 639996
avg 639996/120 = 53332.8
IMO C[/quote]

Can you explain this method in detail, Archit?[/quote]

[url=https://gmatclub.com:443/forum/memberlist.php?mode=viewprofile&un=AkshdeepS][b]AkshdeepS[/b][/url]

total no of combinations which would be formed using digits 1,3,5,7,8 = 5! = 120
and the series of each integer would be of 120/5 = 24 times or say 4!
also a 5 digit no is of the form 10000+10000+1000+100+10+1= 11111
series of 1,3,5,7,8 can be written as ; 4!*(1+3+5+7+8)*(11111) = 639996
then avg = 639996/120 = ~ 53332.8[/quote]

Thanks a lot..Cheers..This is a new learning for me.

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Re: What is the average (mean) of all 5-digit numbers that can be formed [#permalink]
Well,
Since the total terms = 5! = 120
and sum = fix one place so 4! * ( 1+3+5+7+8)*(11111) = 639996
avg 639996/120 = 53332.8
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Re: What is the average (mean) of all 5-digit numbers that can be formed [#permalink]
I understand that there are 120 possible numbers from the 5 digits.

I don't understand anything after that, can someone explain in layman terms?
Re: What is the average (mean) of all 5-digit numbers that can be formed [#permalink]
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