Adding Three One-Digit Numbers (Sums up to 20)

To add three numbers, group any two numbers and find their sum. Then, add the third number to the sum obtained.

For example: Let’s calculate 1 + 2 + 4.

First, group 1 and 2 and find their sum.
 

1 + 2 + 4 = (1 + 2) + 4 = 3 + 4
 

Now, add the third number to the sum obtained.
 

3 + 4 = 7
 

So, 1 + 2 + 4 = 7.