Willow maths set, can you complete these extra challenges?

Willow set maths challenge!

Can you solve these addition problems mentally?

1.  620 + _____ = 690

2.  550 + _____ = 1550

3.  4590 + _____ = 5690

4.  67981 + _____ = 77981

5.  350 + 700 =

6.  7890 + 4000 =

7.  3452 + 700 =

8.  5647 + 5 =

9.  5432 + 700 =

10. 16780 + 30 =

Chilli challenge: Can you create your own mental addition problems?