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Using a Number Line to Add Up to 20

This lesson shows how to add numbers up to 20 by making jumps along a number line. Students learn to start at the first number, jump forward by the second number one hop at a time (or in one big hop), and land on the sum, with extra focus on jumps that cross the friendly landmark of 10.

What Is Number Line Addition?

A number line is a straight line marked with numbers in order, evenly spaced from left to right. It gives you a picture of where every number "lives," which makes addition much easier to see. To add two numbers using a number line, you start at the first number, then hop forward, one space at a time or in one big jump, by however many the second number tells you. Wherever you land is the sum.

This method works well for totals up to 20 because the whole line, from 0 to 20, fits neatly in one view. It is closely related to using counting to add digits up to 20, except instead of counting in your head, you are counting steps along a drawn path.

The Steps for Adding on a Number Line

Follow these steps every time:

Draw or picture a number line marked from 0 to 20.
Find the first number in the addition problem and mark it with a dot.
Count forward that many spaces equal to the second number, one jump per unit.
The tick mark where you land is the answer.

It does not matter which number you start with first, but it is usually quicker to start on the larger number and jump forward by the smaller one, since that means fewer hops.

Worked Example 1: Adding 7 + 5

Start at 7 on the number line. Since you are adding 5, make one jump of 5 spaces to the right. You land on 12, so \( 7 + 5 = 12 \).

Starting at 7 and jumping forward 5 spaces lands on 12.

Worked Example 2: Crossing 10 with 8 + 6

Some jumps are easier to picture in two smaller hops instead of one long one, especially when the total crosses the friendly landmark of 10. Start at 8. First jump 2 spaces to reach 10, then jump the remaining 4 spaces to land on 14. That means \( 8 + 6 = 14 \), because \( 2 + 4 = 6 \).

Splitting the jump at the landmark of 10 makes 8 plus 6 easy to track.

Why the Landmark of 10 Helps

Breaking a jump into two smaller hops that pass through 10 is one of the most useful tricks in number line work. Once you know how far the first hop is to reach 10, the second hop tells you how much further to go. This same idea shows up again once problems grow to include adding with 3 numbers up to 20, where you might jump to 10 first, then keep adding each remaining number one hop at a time.

Number Lines vs. Other Addition Strategies

A number line is one of several ways to picture addition up to 20. Counting on fingers, using ten-frames, or memorizing facts are other common approaches, covered in lessons like adding with digits up to 20. The number line is especially useful because it shows both the starting point and the size of the jump at the same time, which builds a strong sense of how far apart numbers really are, not just what the final answer happens to be.

Tips for Using a Number Line Confidently

Always double-check your starting point before jumping, since a wrong start throws off the whole answer.
Count each tick mark carefully; skipping a mark by accident is the most common mistake.
Break large jumps into two smaller ones through 10 whenever it feels easier.
Practice landing exactly on whole numbers rather than estimating between marks.

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