To anyone who is as confused by this as I was when I first saw it. They basically want to teach a way to “solve” more complicated additions by first “getting to ten”, so if you want to add 8+9 it’s the same as adding 8+2 (from the nine) then you have 10 and then you add the remaining 7. (And 10+7 is obvious).

Also the dots are a visualization of the process (each number represented with as many dots so you “take” two dots from the 9 (turning it into a 7) and “give” them to the 8 (willing it up to 10) so you “made” a 10.

So the right answer here is, as I understand it:

8+2+7=8+9=17