+
0
1
2
3
4
5
6
7
8
9
10
0
0
1
2
3
4
5
6
7
8
9
10
1
1
2
3
4
5
6
7
8
9
10
11
2
2
3
4
5
6
7
8
9
10
11
12
3
3
4
5
6
7
8
9
10
11
12
13
4
4
5
6
7
8
9
10
11
12
13
14
5
5
6
7
8
9
10
11
12
13
14
15
6
6
7
8
9
10
11
12
13
14
15
16
7
7
8
9
10
11
12
13
14
15
16
17
8
8
9
10
11
12
13
14
15
16
17
18
9
9
10
11
12
13
14
15
16
17
18
19
10
10
11
12
13
14
15
16
17
18
19
20

Why does 2 + 9 = 11?

Let's start at 2.

Next, let's count 9 times.

Ready? ... 2, 31, 42, 53, 64, 75, 86, 97, 108, 119.

That's why 2 + 9 = 11.

Mathgrow

0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9