Why do mobile numbers in India have 10 digits ?

The answer, as expected, lies in  Mathematics

 

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From 10 digit mobile numbers, we have  10 x 10 x 10 x 10 x 10 x 10 x 10 x 10 x 10 x 10 = 10,00,00,00,000 = 10 billion numbers  at our disposal.


That is Permutations  & Combinations Chapter at work


So what is  Permutations & Combinations?


When the order doesn't matter, it is a Combination.

Ex. My salad  is a  combination of 

 

When the order does matter it is a Permutation.

Ex. My password is  M@th$

 

Did you know Niue has 4 digit tel no.s ?
Niue an island country, 2,400 kilometers  off New Zealand
As it's  population  is 1,638


Mainland China has 11 digit mobile numbers


Permutations & Combinations is part of Discrete mathematics ...one of the most important courses in Computer Science.