Bheja Fry question

  Question 

All mobile numbers in India are 10 digits.

With 10 digit number, how many mobile subscribers can be supported at any time ??

Answer 

In a 10 digit number, each position can be filled by any of 10 digits ( 0 through 9  )

To find the total number, we multiply the number of possibilities for each position.

==>>   10 * 10 * 10 * 10 * 10 * 10 * 10 * 10 * 10 * 10

==>>   10  ^  10

==>>    10 billion    !!!

The mathematical answer is 10 billion.

But in India, we have prefix restrictions.

Mobile numbers must start with digits  9   8    7  or  6.

To find the total combination,

For the first digit, we have only 4 possibilities. They are 6  7  8  or  9.

For second digit to last digit, 10 possibilities each ( from  0  to   9  )

==>>    4  *   10  ^   9

==>>   4  billion  !!!