Module 3 Calculating
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Can I subtract mentally combinations of one-digit and two-digit numbers?

Example review questions

  • Count back five from 34. Where do you land? Keep counting back in fives. What do you notice?
  • There were 24 biscuits in a box. There are now only 18 left. How many have been eaten? What is the number sentence?
  • Subtract 19 from 74. What did you write, draw or imagine to help you?
  • Find the difference between 17 and 35. How did you find this?
  • What numbers go in the boxes?
    45 = 52 − Empty box
    76 + 5 = 90 − Empty box
    15 − 4 − Empty box = 5
    Empty box − 20 = 64
  • Sam has saved 57p. His sister has saved 83p. How much more money than Sam does his sister have?
  • 12 − 5 = Empty box
    Use this to find 22 − 5.

Teaching guidance

This teaching guidance document suggests some of the key vocabulary, models, images and practical equipment that children should experience and be able to use. It also includes some teaching tips to provide a few starting points for ways of supporting children with this area of mathematics.

DOC file Can I subtract mentally combinations of one-digit and two-digit numbers? - teaching guidance | 154KB new window

Consolidation and practice

These resources are to support children in guided or independent work. Roll over the highlighted resources for a description.

PDF file How to use counting on and back ITP | 102KB new window

SWF file Counting on and back ITP | 34KB new window

PDF file How to use difference ITP | 159KB new window

SWF file Difference ITP | 40KB new window

PDF file How to use bead sticks ITP | 57KB new window

SWF file Bead sticks ITP | 204KB new window

PDF file Springboard 3, Unit 6 Subtraction by counting on from the smaller number | 150KB new window

XLS file Patterns of calculations | 113KB new window

Counting on and back

itp_counting_on_and_back.png

This interactive teaching program (ITP) is an ICT-based tool to support the exploration of numbers to 100 through the simulation of a 100-bead string. Counting on and back ITP allows the teacher or child to add and subtract 1 or 10 to explore different counting and calculation strategies.

Difference

itp_difference.png

This interactive teaching program (ITP) is an ICT-based tool to support the exploration of number. Difference ITP allows the child or teacher to compare two rows of beads and to analyse the calculations they can represent. It can be used to promote the language of addition and subtraction. The ITP operates as a series of animations which show how the rows of beads can be represented by two number lines and then as a single number line with the difference indicated by a 'jump'.

Bead sticks

itp_bead_sticks.png

This interactive teaching program (ITP) is an ICT-based tool to support the exploration of place value. Bead sticks ITP allows the child or teacher to represent numbers (with up to four digits) and explore addition and subtraction. An animation demonstrates the process of grouping and exchange.

Opportunities to use and apply

Possible contexts include:

  • word problems, e.g. Nisha and Charlie play skittles. Nisha scores 38. Charlie scores 50. How much more does Charlie score than Nisha?
  • number sequences, patterns and puzzles, e.g. Find the missing numbers in this sequence:
    A sequence of eight numbers that each decrement by six. The first, fifth and eighth numbers are missing. The sequence is blank, 82, 76, 70, blank, 58, 52, blank.
  • money or measures, e.g. One sunflower is now 38 cm high. Another is 83 cm high. What is the difference between the heights of the sunflowers?
  • graphs and charts, e.g. How many more children walked to school than came by car?
    A pictogram displaying how children travel to school. Three children go by car. 10 children travel by bus. 10 children walk. Five children ride their bikes into school.

Confirming learning

Ask probing questions such as:

  • Can you fill in numbers to make this calculation correct?
    90 − Empty box − Empty box = 55
  • Sam says the answer to 75 − 28 is 53. Kit says it is 47. Who is right? How can you check? What mistake do you think was made?
  • Explain how you would find the difference between 47 and 63.
  • Ben starts at 52 and counts back in nines. Find a number between 10 and 20 that he will land on.
  • Look at this calculation: Empty box2 − 7 = Empty boxEmpty box. Write a digit in each box so that the calculation is correct. How else can you do it? What do you notice?