2
Add with a place value mat
Discover Mathematics P2: Term 2, Lessons 81–90
GoalAdd two-digit numbers with regrouping using tens and ones.
New words
regroup · trade 10 ones for 1 tenones · single objects, the right columntens · bundles of ten, the left column
Explanation
A place value mat has two columns: tens and ones. To add 69 + 23, show 6 tens and 9 ones, and 2 tens and 3 ones. Add the ones first: 9 + 3 = 12 ones. That is 1 ten and 2 ones, so regroup: write 2 in the ones place and add 1 to the tens. Now add the tens: 6 + 2 + 1 = 9 tens. The sum is 92. If you use straws, tie 10 single straws into one bundle of ten.
Worked examples
69 + 23: ones 9 + 3 = 12, so write 2 and carry 1 ten. Tens 6 + 2 + 1 = 9. The sum is 92.
66 + 26: ones 6 + 6 = 12, carry 1 ten. Tens 6 + 2 + 1 = 9. The sum is 92.
37 + 57: ones 7 + 7 = 14, carry 1 ten. Tens 3 + 5 + 1 = 9. The sum is 94.
Class activity
Straw bundles. Use 50 straws or sticks. Show 37 as 3 bundles of ten and 7 singles. Show 57 as well. Put all the singles together, tie ten of them into a new bundle, and count the tens and ones. Does it match 94?
Practice
1
Add 63 + 29.
3 + 9 = 12, carry 1. 6 + 2 + 1 = 9. The sum is 92.
2
Add 56 + 29.
6 + 9 = 15, carry 1. 5 + 2 + 1 = 8. The sum is 85.
3
Add 76 + 15.
6 + 5 = 11, carry 1. 7 + 1 + 1 = 9. The sum is 91.
4
Add 29 + 57.
9 + 7 = 16, carry 1. 2 + 5 + 1 = 8. The sum is 86.
5
Hana has 44 stickers and her friend gives her 39 more. How many stickers does she have?
44 + 39 = 83 stickers.