Add ones to a two-digit number
34 + 3 means keep the 3 tens and add 3 more ones.
34 + 3 = 37 because the tens stay the same and the ones increase from 4 to 7.
Year 2
Add and subtract numbers using concrete objects, pictorial representations, and mentally
Use objects, picture models and simple mental steps to add and subtract ones and tens.
Lesson overview
Number - addition and subtraction
A good method helps you see what changes in the number. When you add or subtract ones, only the ones change. When you add or subtract tens, the tens change. We can show this with base-ten blocks, number jumps and simple number sentences before moving on to more formal written methods.
Add tens to a two-digit number
26 + 20 means add 2 more tens.
26 + 20 = 46 because the ones stay at 6 and the tens increase from 2 tens to 4 tens.
Subtract ones from a two-digit number
42 - 2 means take away 2 ones.
42 - 2 = 40 because the ones move back from 2 to 0.
Worked example
Work out 53 - 10.
- Start with 53.
- Subtract 1 ten.
- The ones stay at 3.
- The tens move from 5 tens to 4 tens.
- So 53 - 10 = 43.
Try it
Look at the picture or jump pattern, then choose the correct answer.
Question 1
Question 2
Question 3
Question 4
Question 5
Common mistakes
Watch for these when you add and subtract mentally.
- Changing the ones as well when only the tens should change.
- Changing the tens when the question only adds or subtracts ones.
- Jumping to a formal written method before understanding what changed in the number.
Related topics
These ideas support mental methods in Year 2.
- Recall and use addition and subtraction facts to 20 fluently, and derive and use related facts up to 100.
- Use the column method for addition and subtraction without carrying or borrowing.
- Solve problems with addition and subtraction using concrete objects and pictorial representations.