Complete subtraction patterns
Preparing your practice…
Go beyond practice with Brilliant’s digital tutor, full interactive curriculum, personalized learning, and progress reports.
Complete subtraction patterns: skill guide
| Objective | Learners find the missing number in a pattern that counts down by 10. |
|---|---|
| Grade | Grade 1 |
| Standard | CCSS.MATH.CONTENT.1.NBT.C.5 |
| Difficulty | Developing · Abstract |
| Representation | Number sequence, Numerical equation |
| Practice format | Interactive, account-free practice with immediate feedback |
Objective
Learners find the missing number in a pattern that counts down by 10.
What this practice covers
Each problem shows five numbers that count down by 10, such as 85, 75, 65, 55, 45, with one number missing. All the numbers are from 20 to 99. Early in a session the blank is always the last number. In the middle of the session it can be any number after the first, and near the end it can be any of the five.
Standards alignment
Supports Common Core: CCSS.MATH.CONTENT.1.NBT.C.5 — Given a two-digit number, mentally find 10 more or 10 less.
Who it’s for
This practice is designed for Grade 1 learners working with two-digit numbers from 20 to 99. It is also useful for older learners who want a short review of counting down by 10.
What to know first
- Learners should read two-digit numerals and know that the tens digit tells how many tens are in a number.
Difficulty and scaffolding
Developing · Abstract stage
Problem representations
- Number sequence
- Numerical equation
Three worked examples
- 84, 74, 64, 54, □: each number is 10 less than the one before it, so the blank is 44.
- 91, 81, □, 61, 51: the tens digit drops by one at each step, so the blank is 71.
- □, 67, 57, 47, 37: the blank comes first, so it is 10 more than 67, which is 77.
Likely misconceptions
- Learners may change the ones digit instead of the tens digit, or count down by 1 instead of by 10. When the blank comes first, some learners take away 10 again instead of finding the number that is 10 more than the next one. Compare two neighboring numbers, name the step, and check that every number has the same ones digit.
Hints and explanations
- 84, 74, 64, 54, □: each number is 10 less than the one before it, so the blank is 44.
- 91, 81, □, 61, 51: the tens digit drops by one at each step, so the blank is 71.
- □, 67, 57, 47, 37: the blank comes first, so it is 10 more than 67, which is 77.
What to practice next
Next, subtract a one-digit number from a two-digit number by counting back.
Editorial review
Reviewed by Brilliant’s curriculum team. Exercises are generated within defined difficulty ranges and checked against verified answer rules.
Complete subtraction patterns FAQs
What is the goal of complete subtraction patterns?
The goal is to find the missing number in a pattern that counts down by 10. A learner should be able to name the step between two numbers and explain why only the tens digit changes.
Should this practice be timed?
No timer is required. First build accurate, understandable strategies. Speed usually improves naturally as learners recognize groups of ten, familiar facts, and repeated patterns.
What should a learner do after a mistake?
Read the pattern aloud, name the step between two numbers that are both shown, and use that step to fill the blank. A short explanation is more valuable than immediately repeating the same guess.
How many problems should be completed at once?
A Quick check has 5 problems and a Practice session has 15. A learner may pause when attention drops. A short, successful session with clear reasoning is more useful than rushing through a longer set.