Mental math: add and subtract multiples of ten

In this mental math lesson, we look at adding and subtracting multiples of ten (20, 30, 40, 50, etc.) to/from a 3-digit number mentally. It is very easy!

First, we do a few of these addition and subtraction problems with the help of a visual model - to show clearly that it is based on place value: we simply add the tens to the existing tens.

Then we solve some more challenging problems, a word problem involving Mathy, my mammoth mascot, and lastly we look at a number pattern of sorts.

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See also

Mental addition - add a 2-digit and a 1-digit number (with regrouping)

Number rainbow & fact families with 12

Math Mammoth Grade 2 curriculum

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