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how many times the digit 7 is written while writing the numbers from 1 to 1,00,00,000?

 how many times the digit 7 is written while writing the numbers from 1 to 1,00,00,000? 

Grade:10

1 Answers

Aman Bansal
592 Points
11 years ago

Dear Sathyaram,

 

First, change the numbers from "1 to 10,000,000" to the boundaries  to 
1) Changing the "boundaries" from   to 
2) Leading zeros wont affect the number of sevens.

As such, we have     

By symmetry, each digit appears exactly as often as each other digit. Every combo of digits gives a viable seven digit number. Thus,

 

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