I have a post on this also, plus a little bit more. Mine also includes multiplying when the numbers are not the same. Here is the first one, it's like what you have here: https://steemit.com/education/@johnwjr7/fun-with-5-s-1 - Please check out @johnwjr7 to see the other, a little more advanced, methods I have on multiplying with 5's.