Easy addition
A little harder
Difficult addition

100

2+1=
3

100

3+5=
8

100

7+4=
11

200

2+3=
5

200

5+1=
6

200

4+2+1=
7

300

1+3=
4

300

4+5=
9

300

6+6=
12

400

1+1=
2

400

4+6=
10

400

2+2+1=
5

500

3+1=
4

500

4+2=
6

500

5+6=
11