Question

Using divisibility test, determine $10000001$ is divisible by $11$.

Answer 1

The rule for the divisibility of $11$ states that if the difference between the sums of the alternate digits of the given number is either $0$ or divisible by $11$, then the number is divisible by $11$.
The sum of alternative digit in $10000001$ are $1+0+0+0=1$ and $0+0+0+1=1$
The difference between two are: $1-1=0$
Hence $10000001$ is divisible by $11$.