A joining situation represents a quantity increasing when another whole-number quantity is added, so the total is the sum of the starting amount and the amount joined, as in . The relationship can be modeled with drawings, ten-frames, number lines, or equations, with attention to distinguishing the initial amount, added amount, and total; problems involve sums within 20 and do not extend to larger numbers or generalized unknown-change cases.
A joining problem tells you that some are there at the start, and then more are added.
Look for:
Example:
There are birds on a fence. Then more birds join them. How many birds are there now?
You can also count on from five times:
So, there are birds altogether.
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