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Permutation & Coombination

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Permutation & Coombination

by gmatmillenium » Sun May 09, 2010 4:15 am
A five digit number is formed using the digits 1,3,5,7 and 9 without repeating any of them. What is the sum of all such possible numbers?

a. 6666600
b. 6666660
c. 6666666
d. 6600000
e. None of the above
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by kstv » Sun May 09, 2010 6:31 am
Total of diff numbers possible = 5!
[spoiler]the smallest no is 13579 and the largest no is 97531
average of 120 nos= (13579+97531)/2
Sum of 120 nos = 111110/2 * 120
= 111110*60[/spoiler]

nice one, some other methods must be tried also.
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by outreach » Sun May 09, 2010 7:35 am
add the diff digits
1+3+5+7+9=25 -(1)

total number of digits that can be formed without numbers repeating=5*4*3*2*1=120
divide 120/5=24 -(2)

(2) gives the number of times each digit repears in unit,hundred,thousand etc position

multiple (1) * (2)=25*24=600 -(3)

multiply (3) by 11111(this number depends on the number of digits)

600* 11111=6666600

A should be the answer
gmatmillenium wrote:A five digit number is formed using the digits 1,3,5,7 and 9 without repeating any of them. What is the sum of all such possible numbers?

a. 6666600
b. 6666660
c. 6666666
d. 6600000
e. None of the above
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