To understand How to do addition on number line, study the following two examples :
Example 1  Solve and show 2 + 3 on number line
Since we have to add 3 to number 2, so we start with number 2 and jump 3 units from number 2 i.e. from 2 to 3, 3 to 4, 4 to 5 and reach on final point i.e. "5". And we know 2 + 3 = 5
Example 2  Solve and show 1 + 6 on number line
Since we have to add 6 to number 1, so we start with number 1 and jump 6 units from number 1 i.e. from 1 to 2, 2 to 3, 3 to 4, 4 to 5, 5 to 6, 6 to 7 and reach on final point i.e. "7". And we know 1 + 6 = 7
