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Door 17 ยท Grade 4

๐Ÿงฉ Number Patterns

A growing pattern gets larger with each term

โ–ถ Play Door 17

Growing Patterns

A pattern is a sequence that follows a rule. In a growing pattern, each term is larger than the one before it.
โ€ข Add patterns: 5, 10, 15, 20, 25 โ€” Rule: +5 each time
โ€ข Multiply patterns: 2, 4, 8, 16, 32 โ€” Rule: ร—2 each time

To find the rule: check what you add or multiply to get from one term to the next. Then use that rule to find the missing term.
Steps to extend a growing pattern:
โ€ข Look at two consecutive terms
โ€ข Find the difference (for add) or ratio (for multiply)
โ€ข Check it works for the next pair too
โ€ข Apply the rule to find the next term

Worked example

Problem: Find the next two terms: 3, 6, 9, 12, ___, ___

  1. Step 1: 6 - 3 = 3, 9 - 6 = 3, 12 - 9 = 3.
  2. Rule = +3 each time.
  3. Step 2: 12 + 3 = 15.
  4. Step 3: 15 + 3 = 18.

Answer: 15, 18

Shrinking Patterns

In a shrinking pattern, each term is smaller than the one before it. The sequence is going down.
โ€ข Subtract patterns: 40, 35, 30, 25 โ€” Rule: -5 each time
โ€ข Divide patterns: 64, 32, 16, 8 โ€” Rule: รท2 each time

Some patterns have a changing difference โ€” this makes them trickier.
Example: 55, 50, 44, 37, 29 โ€” differences are -5, -6, -7, -8 โ€” so the next difference is -9, making the next term 29 - 9 = 20.
Always check if the difference is constant (same) or changing (increasing or decreasing).

Worked example

Problem: Find the next term: 100, 90, 80, 70, ___

  1. Step 1: 100 - 90 = 10, 90 - 80 = 10, 80 - 70 = 10.
  2. Rule = -10 each time.
  3. Step 2: 70 - 10 = 60.

Answer: 60

Input-Output Tables and Rules

An input-output table shows pairs of numbers connected by a rule โ€” like a machine that transforms the input into the output.
The rule can be:
โ€ข Add or subtract: Input 3 โ†’ Output 8 (Rule: +5)
โ€ข Multiply or divide: Input 4 โ†’ Output 12 (Rule: ร—3)
โ€ข Two-step rule: Input 2 โ†’ Output 5 (Rule: ร—2+1)

How to find the rule:
โ€ข Look at the first input-output pair
โ€ข Try simple operations (+, -, ร—, รท)
โ€ข Test your rule on at least two more pairs
โ€ข If it works for all pairs, you have the rule

Once you know the rule, you can find any output for any input.

Worked example

Problem: Find the rule: Input 5 โ†’ 15, Input 8 โ†’ 24, Input 10 โ†’ 30. What is the output when input = 6?

  1. Step 1: Try ร—3: 5ร—3=15 (yes!), 8ร—3=24 (yes!), 10ร—3=30 (yes!).
  2. Rule = ร—3.
  3. Step 2: When input=6, output = 6ร—3 = 18.

Answer: 18