A way that I would teach someone something that I learned in math this year to someone else is simple. I would start by writing everything out so that they have a visual of what I am teaching them. I would also use a visual of a real world situation so that it relates to something they would understand. Teaching someone younger than you means they probably will not understand as easy as you understood it so, I would be very slow and make sure if they are confused to help them. I would also make sure not to be too bossy, understanding that they may not understand and that is ok.
