New
New
Solve problems by adding and subtracting to or from 3-digit numbers
I can solve problems by adding to and subtracting from 3-digit numbers.
Lesson 13 of 15
New
New
- Year 3
Solve problems by adding and subtracting to or from 3-digit numbers
I can solve problems by adding to and subtracting from 3-digit numbers.
Lesson details
Key learning points
- Number lines can record the steps in our thinking when we are partitioning to add and subtract.
- The 1s digit does not change when you add or subtract a multiple of ten.
- Number facts to 10 help when crossing the 10s and 100s boundaries.
Keywords
Bridge - Bridging is a strategy which uses addition or subtraction to cross a number boundary.
Partition - Partition means splitting an object or value down into smaller parts.
100s boundary - The 100s boundary is the point at which the numbers change into 100s numbers, or from one set of hundreds to another.
Common misconception
Pupils may struggle to partition 10s numbers to help them bridge a 100s boundary.
Encourage pupils to calculate the number of tens needed to add or subtract to the 100s number, then add or subtract the remainder.
Pupils will need to use number lines to represent their thinking. Base ten blocks may also be helpful for some pupils, although these do not feature in the lesson. They can be used alongside number lines to support pupil learning.
Teacher tip
Licence
This content is © Oak National Academy Limited (2025), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).
Lesson video
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Prior knowledge starter quiz
6 Questions
Q1.How should you partition 5 to calculate 98 + 5?
How should you partition 5 to calculate 98 + 5?
add 3 then add 2
add 4 then add 1
Q2.Which calculations cross a 100s boundary?
Which calculations cross a 100s boundary?
190 − 30
220 + 30
Q3.What is 230 + 30?
What is 230 + 30?
Q4.270 − 40 =
270 − 40 =
Q5.Which calculation is shown by the number line representation?
Which calculation is shown by the number line representation?
397 + 3 = 403
397 + 5 = 403
396 + 6 = 403
Q6.Use the number line to find the missing number. 510 − ___ = 460
Use the number line to find the missing number. 510 − ___ = 460
10
20
40
Assessment exit quiz
6 Questions
Q1.How should you partition 60 to calculate 160 + 60?
How should you partition 60 to calculate 160 + 60?
add 20 then add 40
add 30 then add 30
Q2.How should you partition 60 to calculate 210 − 60?
How should you partition 60 to calculate 210 − 60?
subtract 20 then subtract 40
subtract 30 then subtract 30
Q3.245 + 20 =
245 + 20 =
Q4.320 − 40 =
320 − 40 =
Q5.Colin the cat is 410 cm high in a tree. He climbs down 50 cm. How high is he now?
Colin the cat is 410 cm high in a tree. He climbs down 50 cm. How high is he now?
350 cm
460 cm
Q6.Katya is in a tree. She climbs down 30 cm. She is now 288 cm high. How high was she when she started? cm
Katya is in a tree. She climbs down 30 cm. She is now 288 cm high. How high was she when she started? cm
