Math

My learning goal is multiples of 100 that add up to 10000, e.g.  400 + 600, 300 + 700.

I have learnt recall subtraction facts to 20 e.g. 19-6, 17-?= 12

My next steep is to  Recall addition and subtraction facts to 20 with change unknown,

e.g. 9 + _ =15 ,  13 - _ = 8