mobile number consists of 10 digit first 4 digit 9 9 7 and 9 make the smallest mobile number by using only 1 digit twice from 83560
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Suppose you are the coach of a team of 4 players. You need appoint a captain and a vice-captain for your team. In how many ways can you do this?
P1 + P2P1 + P3P1 + P4P2 + P1P2 + P3P2 + P4P3 + P1P3 + P2P3 + P4P4 + P1P4 + P2P4 + P3
Thus you can have 12 such combinations. First you find out the number of people that can be made the captain (4). Then you multiply with the number of people that can be made vice captain (3, as 1 has already been made the captain). You multiply and get the answer as 12.
The same logic is used for phone numbers. If we had a 5 digit mobile number, each digit place could be filled by ten different numbers, from 0–9. Then total number of phone number which were possible = 10*10*10*10*10 = 1,00,000.
This would be insufficient for a country with population of 120 crores. A 10-digit cell number offers us a capacity to have 1,000 crore phone numbers, which is far more than what our country can ever achieve. Hence, a 10-digit mobile number.
P1 + P2P1 + P3P1 + P4P2 + P1P2 + P3P2 + P4P3 + P1P3 + P2P3 + P4P4 + P1P4 + P2P4 + P3
Thus you can have 12 such combinations. First you find out the number of people that can be made the captain (4). Then you multiply with the number of people that can be made vice captain (3, as 1 has already been made the captain). You multiply and get the answer as 12.
The same logic is used for phone numbers. If we had a 5 digit mobile number, each digit place could be filled by ten different numbers, from 0–9. Then total number of phone number which were possible = 10*10*10*10*10 = 1,00,000.
This would be insufficient for a country with population of 120 crores. A 10-digit cell number offers us a capacity to have 1,000 crore phone numbers, which is far more than what our country can ever achieve. Hence, a 10-digit mobile number.
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