Add a 2-digit number and a single-digit number mentally - no regrouping

In this lesson for 1st grade, I show with a visual model how EASY it is to add sums such as 23 + 6 or 54 + 3 mentally.

You simply add the ones, and the tens do not change. To solve 23 + 6, add 3 + 6 = 9, and the answer is 29. Children will easily get this idea when shown a visual model.

We also add numbers "in boxes" — in other words, by writing one number under the other, or adding in columns.

The lesson also includes an initially silly word problem (by Mathy my mascot mammoth), and some comparisons that require a bit of algebraic thinking.

Note that the sums in this lesson do not require regrouping (carrying) — we study that process in another lesson.

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See also

Two-digit mental addition — online practice

Mental math trick with nine and eight

Math Mammoth Grade 1 curriculum

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