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(#M40032207) OTHERS Numerical Ability question permutations and combinations Keep an EYE

Q. How many 7 digit telephone numbers can be formed using the numerals 0 to 9?

Asked In Others shrishma L (11 years ago)

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ASHISH KATIYAR  (11 years ago)

0 to 9 are total 10 numbers so we can fill 7 places with all 10 numbers so total no of telephone nos will be 10^7.
but this will also contain telephone no as 0000000 so subtract 1 from total numbers hence
total no of telephone nos will be (10^7)-1

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ankita  (11 years ago)

9*10^6..
...

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Krishna Charan  (11 years ago)

The last six digits can be anything from 0 to 9, so we can place those 10 numbers in 6 positions with repetition, so the no. of ways =
10*10*10*10*10*10 = 10^6
First digit should not be 0, so only 9 digits for 1 position, the no. of ways = 9
So the answer is 9*(10^6)

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DHAKAD NEETENDRA SINGH  (11 years ago)

if digits are not repeated then 9c7*7!=181440
if digits are repeated then 10^7

because in the phone number can start with 0

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