Question
How many $8-$digit numbers are there in all$?$
✓
Answer
There are $10$ digits i.e., $0, 1, 2, 3, 4, 5, 6, 7, 8, 9.$
We cannot use $‘0’$ at the place having the highest place value in $8$ digit numbers.
So, we can use only $9$ digits at the place having the highest place value in $8$ digit numbers.
Also, we can use $10$ digits at the remaining places in $8$ digit numbers So, total numbers of $8-$digit
numbers $= 9 \times 10 \times 10 \times 10 \times 10 \times 10 \times 10 \times 10 = 90000000$
We cannot use $‘0’$ at the place having the highest place value in $8$ digit numbers.
So, we can use only $9$ digits at the place having the highest place value in $8$ digit numbers.
Also, we can use $10$ digits at the remaining places in $8$ digit numbers So, total numbers of $8-$digit
numbers $= 9 \times 10 \times 10 \times 10 \times 10 \times 10 \times 10 \times 10 = 90000000$
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