In this lesson we add and subtract whole tens, such as 50 + 40 or 90 - 70, using mental math. First, students can use pictures (base ten blocks) to do that, but I'm sure they will soon notice the SHORTCUT: you can simply work with the number of tens the same way you add or subtract single-digit numbers. That way, 50 + 40 becomes 5 tens + 4 tens, which is 9 tens.
Lastly, Mathy gives us a challenging addition problem to solve... making TENS helps a lot!
Check out also my workbook Math Mammoth Place Value 1 at http://www.mathmammoth.com/place_value_1.php
Tagged under: tens,add,subtract,1st grade,math,place ,multiples ten,tens,mental math
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