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mandy
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Ps permutation / combination 31 Aug 2005, 17:45
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hello

How many 5 DIGITS telephone numbers exist in which at least one of the digit is repeated

plz explain your work and logic
thanks :)



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ranga41
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Ps permutation / combination Updated on: 31 Aug 2005, 19:56
Originally posted by ranga41 on 31 Aug 2005, 19:02.
Last edited by ranga41 on 31 Aug 2005, 19:56, edited 1 time in total.
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Total no of 5 digit numbers = 10^5

Total no with no repetition = 10x9x8x7x6

So the answer = 100000-30240 = 69760

(considering 00000, 0000x, etc as numbers too)
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Ps permutation / combination 31 Aug 2005, 19:22
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Total number of digits with alteast 1 repeated = Total number of digits with repetition - total number of digits with no repetition

Total number of digits with repetition = 10^5 = 100000
Total number of digits with no repetition (treating 0 on par with the other digits) = 10*9*8*7*6 = 30240

SO number of digits with atleast one repetition = 69760
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mandy
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Ps permutation / combination 02 Sep 2005, 17:16
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thanks for your feedbacks the OA is 62784

Because it is assumed that O can not be the first digit

but Plz can anyone explained me this : Total number of digits with alteast 1 repeated = Total number of digits with repetition - total number of digits with no repetition

I don 't understand the total number of digit with repetition minus the total of no repetition give the at least one repeated

thanks


:)
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Ps permutation / combination 03 Sep 2005, 13:20
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Quote:
the total of no repetition give the at least one repeated
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is: one , two, three, four, five repeated.

The above plus 0 repeated, you get all possible 5 digit numbers allowing repetition.
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rthothad
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Ps permutation / combination 03 Sep 2005, 19:50
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mandy
thanks for your feedbacks the OA is 62784

Because it is assumed that O can not be the first digit

but Plz can anyone explained me this : Total number of digits with alteast 1 repeated = Total number of digits with repetition - total number of digits with no repetition

I don 't understand the total number of digit with repetition minus the total of no repetition give the at least one repeated

thanks


:)
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Mandy, Can you verify the OA - Is it 72784 or 62784
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mandy
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Ps permutation / combination 04 Sep 2005, 08:53
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rthothad
mandy
thanks for your feedbacks the OA is 62784

Because it is assumed that O can not be the first digit

but Plz can anyone explained me this : Total number of digits with alteast 1 repeated = Total number of digits with repetition - total number of digits with no repetition

I don 't understand the total number of digit with repetition minus the total of no repetition give the at least one repeated

thanks


:)

Mandy, Can you verify the OA - Is it 72784 or 62784
Show more


Rthothad the OA is 62784 coming from 90 000- 27216



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