How does khan academy have automatic syntax validation

Keep your choice of a major there is probably no single correct choice.

There is a simple pattern for determining if a binary number is odd. what is it and why does this pattern occur? how many bits would you need if you wanted to have the ability to count up to 1000? how high could you count in binary if you used all 10 of your fingers as bits? (finger up means 1, finger down means 0)

Worth 50 points answer them bc i am not sure if i am wrong