Understand the idea.
Add the parts
Use tens and ones to keep a two-digit calculation clear. For , join three tens and two tens, then four ones and three ones. You can also start at , add , then add .
Choose a short route
Choose jumps that suit the numbers. Adding a small amount may take only a few forward jumps. To find , count the short distance from to ; counting back forty-nine times would take much longer.
See the method in action.
Add two two-digit numbers
Find 46 + 21.
Worked solution
- 1
Split the number being added.
Twenty-one contains two tens and one one.
- 2
Add the tens.
Adding two tens changes four tens into six tens.
- 3
Add the one.
Both parts of twenty-one have now been added.
67
Find a small difference
Find 62 − 58.
Worked solution
- 1
Count from fifty-eight to the next ten.
The first forward jump covers two of the missing ones.
- 2
Count from sixty to sixty-two.
The second jump reaches the starting amount in the subtraction.
- 3
Add the two jumps.
The distance from to is the difference, so .
4
Try it yourself.
Check your understanding
Find 35 + 12.
Show answer & reasoning
47
Split twelve into ten and two. First , then ; both parts of twelve are included.
Keep practising
6 worksheet questions
Read the questions online
- Find .
- Find .
- Find .
- Find .
- There are 38 children inside and 7 outside. How many children are there?
- A ribbon is 51 cm long. Another is 48 cm long. How much longer is the first?
Read the worked solutions
- Find .
, then add 2 more.
32 - Find .
; .
68 - Find .
Take 3 tens from 7 tens; keep the 6 ones.
46 - Find .
; .
33 - There are 38 children inside and 7 outside. How many children are there?
.
45 children. - A ribbon is 51 cm long. Another is 48 cm long. How much longer is the first?
48 to 50 is 2 cm; 50 to 51 is 1 cm; cm.
3 cm.
Curriculum reference & lesson scope
Australian Curriculum v9 and SA Curriculum Mathematics
Facts within 20; one-/two-digit calculations; partitioning; related facts; missing numbers; checking.
Official curriculum source ↗