New
New
Year 2

Add and subtract 1 to and from a 2-digit number crossing the tens boundary

I can add and subtract one to and from a two-digit number crossing the tens boundary.

New
New
Year 2

Add and subtract 1 to and from a 2-digit number crossing the tens boundary

I can add and subtract one to and from a two-digit number crossing the tens boundary.

Lesson details

Key learning points

  1. Finding one more is the same as adding one; finding one less is the same as subtracting one.
  2. Numbers that are one more or one less than each other have a difference of one.
  3. When one is added to a number with a ones digit of 9, the next multiple of ten will be reached.
  4. When one is subtracted from a multiple of ten, the number reached will have a ones digit of 9
  5. When one ten is changed for ten ones, or ten ones for one ten, it is called regrouping.

Common misconception

Children may have difficulty finding one less than a multiple of ten saying, for example, one less than 60 is 69.

Refer to the order of the decades counting forwards and backwards and encourage visualisation of the decades on number lines and one hundred squares to support this. Help children to generalise about the number before a decade number ending in 9

Keywords

  • One more - One more is when there is a greater amount by one or another item in the set.

  • One less - One less is when there is a smaller value by one.

  • Difference - The result of subtracting one number from another, How much one number differs from another.

  • Decade - A group of ten numbers below one hundred, each with the same tens digit.

  • Regroup - To exchange ten ones for one ten or one ten for ten ones in order to calculate more easily.

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

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6 Questions

Q1.
Which of the following two numbers have a difference of 1?
57 and 59
34 and 36
Correct answer: 89 and 88
Q2.
Sam gathers Base 10 blocks to show one more than 47 Which image shows his Base 10 blocks?
An image in a quiz
An image in a quiz
Correct Answer: An image in a quiz
An image in a quiz
Q3.
Which number completes the stem sentences? 58 is equal to plus 1
Correct Answer: 57, fifty-seven, fifty seven
Q4.
Choose which equation represents this part-part-whole model, then solve it.
An image in a quiz
Correct answer: 69 - 1 = ___
69 + 1 = ___
Q5.
Alex represents this number. Which place value chart represents the number that is one less?
An image in a quiz
An image in a quiz
Correct Answer: An image in a quiz
An image in a quiz
An image in a quiz
An image in a quiz
Q6.
Solve each equation by matching correctly.
Correct Answer:___ = 34 + 1 ,35

35

Correct Answer:34 = ___ + 1,33

33

Correct Answer:___ - 1 = 34 ,35

35

6 Questions

Q1.
Which decade is missing on the number line?
An image in a quiz
Correct answer: the fifties
the sixties
the forties
Q2.
Alex adds 1 one to these Base 10 blocks. Which picture shows the number he now has?
An image in a quiz
An image in a quiz
Correct Answer: An image in a quiz
An image in a quiz
An image in a quiz
Q3.
Alex taps one less than the number shown. What number does he tap?
An image in a quiz
Correct Answer: 59, fifty-nine, fifty nine
Q4.
Sam thinks of two numbers with a difference of 1 One of her numbers is 30 What could the other number be?
Correct Answer: 31, 29
Q5.
Which numbers are missing?
An image in a quiz
61 and 62
62 and 63
Correct answer: 59 and 60
Q6.
Which equation represents the relationship between the numbers on the number line.
An image in a quiz
59 + 60 = 1
Correct answer: 59 + 1 = 60
Correct answer: 60 - 1 = 59
60 - 59 = 1