Math // Addition & Subtraction

Subtracting multiples of 10

Subtract multiples of 10 (10–90) from multiples of 10 using place value strategies

Ages
6 to 7
Type
Method
Builds on
2 topics
Leads to
0 topics
Standards
1 code

Quick check

Can the learner quickly work out '80 − 50' or '70 − 40' in their head by thinking about how many tens are left?

Ask this to see whether the topic is secure.

Topic // Mastery

What mastery looks like

What a learner can do once this topic is secure.
  • Calculate 70 − 30 = 40
  • Use base-ten blocks to show 80 − 50 = 30
  • Explain that subtracting tens is like subtracting the tens digits

Topic // Map

Where this fits

What to learn first and what this topic opens up, with the reason for each link. Required links come first.
  • RequiredMust come first
  • HelpfulHelps, but not essential

Before this

2 topics
  • Subtraction as taking away or separatingRequired

    Addition & Subtraction // Ages 4 to 6

    Subtracting multiples of 10 requires understanding subtraction

  • The multiples of 10Required

    Number Representation & Place Value // Ages 6 to 7

    Subtracting multiples of 10 requires understanding decade numbers as tens

You are here

Subtracting multiples of 10

Ages 6 to 7 // Method

Leads to

0 topics

Nothing in the catalogue builds on this topic yet. Browse Addition & Subtraction

Topic // Research-informed

Teaching notes

From the Marble Skill Taxonomy. These notes have not been validated in classrooms, so treat them as a starting point for your own judgement.

The approach

Teach subtracting multiples of ten (e.g. 70−30) through unitising: a decade number is a count of tens, so 70−30 is seven tens minus three tens = four tens. The known fact 7−3=4 is reused at the scale of tens, so the '0' in 40 carries real place meaning rather than being appended as a trick. Removable tens-materials, bead strings, and number lines that jump in tens make this visible; contrasting 70−3 with 70−30 exposes whether the child is tracking the unit.

Common misconceptions

  • Dropping the ten-unit: subtracting 7−3=4 and answering 4 instead of 40
  • Treating the zero as a spelling trick ('add a zero') with no unit meaning
  • Counting back in ones (70,69,68…) and losing track
  • Confusing 70−3 with 70−30 because the unit isn't tracked

Useful representations

  • Ten-rods / base-ten tens (remove whole rods)
  • Bead string in tens or 100-bead frame
  • Number line with jumps of ten
  • Hundred square (move up in tens)
  • Place-value chart showing the tens column

Teaching practices

  • Build on 'the multiples of ten represent one-to-nine tens': treat 70−30 as 7 tens − 3 tens (NCETM Spine: derived facts, e.g. 30+70 from 3+7)
  • Reuse the known within-ten fact explicitly — connect 7−3 to 70−30 so the child sees the same subtraction at a larger unit
  • Represent with ten-rods and with a number line that jumps in tens, so subtraction of tens is a small number of large jumps
  • Ask the child to explain that subtracting tens is like subtracting the tens digits because each unit is a ten — meaning behind the zero
  • Contrast 70−3 with 70−30 to expose whether the child is tracking the unit

Activities to try

  1. 1

    Removing whole tens from a tens-only mat

    Why it works: Subtracting multiples of ten is the same subtraction as the known single-digit fact, spoken in units of ten; the zero in the answer is a real placeholder showing zero ones, which keeps the 4 in the tens place. It is not decoration.

    1. Lay out seven ten-rods (or ten-sticks/strips of ten) to represent 70.
    2. For 70 − 30, physically remove three whole rods and say the running count aloud: 70 → 60 → 50 → 40.
    3. Name what is left as 'four tens, which is 40', pointing at the four rods rather than counting individual cubes.
    4. Say the matching single-digit fact: 'seven tens minus three tens is four tens, just like 7 − 3 = 4.'
    5. Repeat for 80 − 50 (eight rods, remove five, leaving three = 30) and 90 − 60 (nine rods, remove six, leaving three = 30), each time removing whole rods and stating the answer in tens.
  2. 2

    Contrasting 70 − 3 with 70 − 30

    Why it works: The size of the unit being removed matters: subtracting tens and subtracting ones are different because each ten is worth ten ones.

    1. Work 70 − 30 by removing three whole ten-rods; record the answer (40) and the running count.
    2. Rebuild 70 with seven ten-rods, then unbundle (or exchange) one ten-rod for ten single cubes; use these to work 70 − 3 by removing three single cubes.
    3. Compare the two results: 70 − 30 = 40 (a big change) versus 70 − 3 = 67 (a small change).
    4. Explain in words why removing three tens changes the number far more than removing three ones.
  3. 3

    Linking the known fact on a reference chart

    Why it works: Each decade subtraction reuses a single-digit fact at the scale of tens, so the known fact gives the answer directly.

    1. Look at 70 and state that it is '7 tens'.
    2. Alongside 7 − 3 = 4, write 7 tens − 3 tens = 4 tens = 40.
    3. Do the same for other decade pairs (e.g. 8 − 5 = 3 beside 80 − 50 = 30), reading each as a statement about tens.

Topic // Standards

Curriculum standards

Codes for the curriculum statements this topic maps to. Each publisher owns its standard text.
Common Core State Standards for Mathematics
1.NBT.6

Math // Addition & Subtraction

More in Addition & Subtraction

All 52 topics