Open Number Line
Hello PT,
Trying to teach 6 + _______=20 Using an open number line to find the answer. But my kids are having trouble with this. Aside from the usual of making the lines on it...and subtracting from the 20, is there another easier way of teaching this? 
Not sure if this will help ...
Make a friendly number, 10, then easier to add 6 + 4 = 10, then 10 + 10 =20 Can go either direction (addition or subtraction) on s number line  whatever strategy is easier for the learner. That’s how I’d teach it. 
I bet they're struggling
with the concept of subtracting to add. That is, they're not applying/understanding the fact family idea that if 6 + ___ = 20, then 20  6 = ___.
I would do it both ways (one is a check on the other) and have them get double practice, plus learn the application of fact families. So first, count UP. Start at 6, then up until you get to 20. First, one at a time Then, as mentioned previously 6 +4=10, 10+10=20 If the problem was 6 + __ = 22, then you'd do all of the above plus add a step at the end. 6 +4 = 10 10 +10 = 20 20 +2=22 (add 4+10+2 to get the answer 16) Do the reverse. Start with 20. Count down by ones. Then group to make "easy" numbers. 
I would add by 10's until you got close to the target number and count by ones. 6+10 moves to 16, then 4 more jumps to get to 20.

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