Counting by 10's
20 - 10 =
2 + 4 + 6 =
35 + 20 =
any problem adding 9, 5 and 4 in a different order.
2 + 8 + 3 =
50 - 20 =
any problem adding 1, 9 and 8 in a different order.
6 + 4 + 9 =
27 + 40 =
any problem adding 10, 3 and 5 in a different order.
3 + 6 + 7 =
89 + 10 =
any problem adding 29, 87 and 99 in a different order.