Question

How many $8-digits$ numbers are there in all?

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Answer 1

We know that the $10$ digits are $0,1,2,3,4,5,6,7,8and9$.

The first digit can be any digit but $0$, the next $7$ digits can be any of $0-9$

So, the total number of 8 digit numbers $=9\times 10\times 10\times 10\times 10\times 10\times 10\times 10=$ $90000000$

Therefore, $90000000$ eight digit numbers are there in all.