How many numbers are there?
Number Theory
Level
pending
How many positive -digit numbers are there that do not start nor end with ?
The answer is 7200000.
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1 solution
The first digit has 8 possibilities and the last digit has 9 possibilities. The second, third, fourth, fifth, sixth, and seventh digits has 1 0 possibilities. To conclude, there are 8 ⋅ 9 ⋅ 1 0 5 = 7 2 0 0 0 0 0 numbers with the desired property.