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This problem is based on non-terminating, repeating decimal points.
Let \$n\$ be any integer, say \$7\$. Then, \$1/n = 1/7 = 0.142857142857142857...\$
We see a pattern like, 0. 142857 142857 142857 ...
In this 142857 part is repeating always, which has length of \$6\$. Or, if \$n = 11\$, then \$1...