Adding with Whole Tens
This is a complete lesson for 1st or 2nd grade about adding a twodigit number and a multiple of ten, such as 58 + 30. Students first use a visual model for tens and ones to add. Then the lesson explains a strategy for doing such sums: break the 2digit number into parts before adding. The lesson has many exercises, word problems, a pattern exercise, and a fun puzzle.
1. The numbers are shown with tensticks and onedots. Write the sums.








Adding whole tens and
Break down the other

2. Add. Break the second number into tens and ones first. Then add the tens.
a. 10 + 34 = _______ (10 + 30 + 4) 
b. 10 + 28 = _______ (10 + _____ + _____ ) 
c. 20 + 24 = _______ (20 + _____ + _____ ) 
d. 30 + 21 = _______ 
e. 50 + 17 = _______ 
f. 40 + 33 = _______ 
g. 60 + 23 = _______ 
h. 30 + 37 = _______ 
i. 70 + 25 = _______ 
3. Add. Break the first number into tens and ones first. Then add the tens.
a. 45 + 20 = _______ (40 + 5 + 20) 
b. 27 + 20 = _______ ( _____ + _____ + 20 ) 
c. 45 + 40 = _______ ( _____ + _____ + 40) 
d. 46 + 30 = _______ 
e. 16 + 50 = _______ 
f. 38 + 60 = _______ 
g. 20 + 77 = _______ 
h. 58 + 40 = _______ 
i. 40 + 39 = _______ 
4. Explain in your own words how you can mentally add 21 + 60.
5.
Fill in the chart of doubles again, and notice its PATTERN. 

6. Isabella got 30
books out of the library, and read half of them in two
days. How many books does she have left to read?
7. Gwen and Mom went
shopping. They bought shoes for $40, a top for $10,
and a skirt for $20.
Mom paid half of the cost and Gwen paid the rest.
How much did
Gwen pay?
8. Jacob had $61. Then he bought a toy for $30. How much money does he have left?
9. Fill in the missing numbers and find how many tens were added.
a. 12 + _____ = 22 12 + _____ = 52 12 + _____ = 42 
b. 45 + _____ = 65 45 + _____ = 55 45 + _____ = 75 
c. 23 + _____ = 63 23 + _____ = 53 23 + _____ = 93 
10. Add 10,
20, 30, or 40. In the box below the number, write “E” if the number is even,
and “O”, if the number is odd. What
do you notice?
+ 10

+ 20

+ 30

+ 40

+ 40

+ 30

+ 20

+ 10


This lesson is taken from Maria Miller's book Math Mammoth Add & Subtract 2B, and posted at www.HomeschoolMath.net with permission from the author. Copyright © Maria Miller. The lesson addresses the following Common Core standard for 1st grade: 1.NBT.4.
Math Mammoth Add & Subtract 2B
A selfteaching worktext for 2nd grade that covers mental addition and subtraction with twodigit numbers, and regrouping in addition and subtraction (carrying & borrowing).
Download ($5.65). Also available as a printed copy.