Question 22
$2^x$ means that 2 is used as a factor x times. For example, $2^4$ means $2\times 2\times 2\times 2=16$. We say that $2^4$ ends in 6 and that $2^4$ has a units digit of 6. If $2^{1997}$ is multiplied out, determine the units (ones) digit of the product.