How do you multiply a 2 digit number by a 2 digit number?

Answer 1

If the two numbers are written as ab and cd then these represent the decimal numbers (10a + b) and (10c + d) and their product is 100*a*c + 10*a*d + 10*b*c + c*d = 100*a*c + 10*(a*d + b*c) + c*d. This is the result that you would get if you used partial products (also called chunking).