Subtract by counting up; choose a strategy

Maths Year 2
This unit is part of Year 2 Flexible Maths Blocks More Addition and Subtraction and Year 2 Maths Planning More Addition & Subtraction

Planning and Activities

Day 1 Teaching
Say you have 52p and spend 47p. Mark 52p on a 0–£1 penny line. Explain: We can count up to find a difference. Mark on 47p, and cross out pennies up to 50p, then to 52p: 3p + 2p is 5p left. Repeat for £63 – £56, hopping £4 to £60, then another £3 to find the £7 difference.
Group Activities
-- Discover how much money is left by calculating differences using a penny line.
Day 2 Teaching
Show a toy frog and agree a name. Explain that maths Frog helps us subtract by hopping up the number line to find a difference. Model how Frog hops from 37 to 45 on the bead bar to solve 45 – 37. Repeat several times with other problems on beaded lines.
Group Activities
-- Calculate the difference between two 2-digit numbers by counting up with Math Frog.
-- Play ‘snatch the match’: subtract two 2-digit numbers by counting up with Maths Frog.

Day 3 Teaching
Write 53 - 47 on the board and read it as 53 subtract 47. Model counting back; then use Frog to find the difference. Compare the two strategies. Use Frog to solve 54 – 48, 23 – 17 and 65 – 54.
Group Activities
-- Solve subtractions using beaded, landmarked or empty number lines.
-- Suggest the subtraction by watching Maths Frog complete jumps on a bead bar.

Day 4 Teaching
Show how solve 62p – 47p using a 0–£1 penny line. Cross out up to 47p. Then demonstrate drawing 3 hops: 47 to 50, then 50 to 60 and 60 to 62. Write 85 – 68 and show how Maths Frog can help us count up. Repeat with 61 – 47 on a landmarked line.
Group Activities
Use the ‘Frog’s Busy Day’ in-depth problem-solving investigation below as today’s group activity.
Or, use this activity:
-- Solve subtractions of 2-digit numbers with answers greater than 10.

Day 5 Teaching
Discuss how we may want to solve 53p – 11p and 60p – 47p in different ways. The first can easily be done by counting back. The second may be more easily solved with maths frog. Repeat to choose a different strategy for 62 – 25 and 67 – 25.
Group Activities
-- Investigate an efficient method for subtracting (counting up or back).

You Will Need

  • 0–£1 penny lines and 0–£1 landmarked lines (see resources)
  • ‘How much money is left?’ sheet (see resources)
  • ‘Finding change’ sheet (see resources)
  • Coins
  • Pen with a price level of 59p, other items with price labels of 55p, 57p, 58p, 56p
  • Maths Frog (toy)
  • 100-bead bar
  • Additional activity sheets (see resources)
  • Dice (some 1–8 and some 1–6)
  • Counters
  • Whiteboards and pens

Mental/Oral Maths Starters

Day 1
Pairs to 10 (pre-requisite skills)

Day 2
Add to the next 10 (pre-requisite skills)

Day 3
Identify 2-digit numbers on a landmarked line (pre-requisite skills)

Suggested for Day 4
Count on and back in tens (simmering skills)

Suggested for Day 5
Telling time to the quarters (simmering skills)

Worksheets

Day 1
Find how much money is left over when children buy a drink by finding the difference.

Day 2
Use Frog (counting up) to solve subtractions.

Day 3
Subtract 2-digit numbers by counting up.

Day 4
Use number lines to find the difference by counting up.

Day 5
Choose an efficient strategy to solve subtractions.

Mastery: Reasoning and Problem-Solving

  • Find the change from 50p if I spend 38p using a 0–50 penny line.
  • Draw Frog’s hops on a number line to show the difference between 43 and 36.
    Draw Frog’s hops on a number line to show 65 – 58.
  • Tell Frog how many hops he will need to do for each of these subtractions:
    a) 45 – 38
    b) 62 – 45
    c) 71 – 65
    d) 34 – 18
    Now use Maths Frog to help you solve each one.
    Were you right about the number of hops each time?
  • Explain which method you would choose to do each of these subtractions:
    47 – 24
    63 – 47
    74 – 64

In-depth Investigation: Frog's Busy Day
Children look for numbers which have a difference of 5 using Frog to help.