Mathematics
Intermediate
40 mins
Teacher/Student led
+80 XP
What you need:
IWB/Projector/Large Screen

Rules for Patterns Using Words and Tables

Build a table showing how a growing pattern develops, then write a rule in words to find any term without drawing all the steps. Use the rule to leap to far terms quickly.

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    1 - Getting Started ~4 mins

    Illustration for Getting StartedHere is a growing tile pattern: pattern 1, then pattern 2, then pattern 3, each one a little bigger than the last. Pattern 1 uses 3 tiles, pattern 2 uses 5 tiles, pattern 3 uses 7 tiles.

    Big question

    Now the big question: how many tiles would pattern 10 need? Could you work it out without drawing all ten patterns?

    2 - Watch and Notice ~8 mins

    To help us, we use a machine: a machine that takes a term-number in and gives a value out using a hidden rule. We feed in 1, 2, 3 and read off the values it hands back, then we work out the hidden rule.

    Our first machine: terms 1, 2 and 3 give us 3, 5 and 7

    Watch as we feed the term-numbers 1, 2 and 3 through the machine and read off the values 3, 5, 7. Look at the jump between each value: 3 to 5 is up 2, and 5 to 7 is up 2 again, so it grows by 2 for every extra term. That means term 1 has 1 lot of 2, term 2 has 2 lots of 2, term 3 has 3 lots of 2 — so the value is 2 times the term. Check term 1: 2 × 1 = 2, but we have 3, so there is 1 extra. The rule is tiles = 2 × term + 1.

    The times-three rule

    Before I send these through, predict the jump: how much do you think the values go up by each time? Here the machine takes a term-number and gives back three times as much: term 1 gives 3, term 2 gives 6, term 3 gives 9 — up 3 each time, so 3 lots for every extra term. Check term 1: 3 × 1 = 3, and we have 3, so there is nothing extra to add. The rule is tiles = 3 × term.

    The times-four minus one rule

    Predict the jump again before we feed these in. The values are 3, 7, 11, 15 — going up in fours, so 4 lots for every extra term, and the value is 4 times the term. Check term 1: 4 × 1 = 4, but we have 3, so we are 1 short — we take one off. The rule is tiles = 4 × term − 1. Notice how the step between values matches the number we multiply by.

    3 - Try It Together ~10 mins

    Today we work through this growing pattern together: term 1 gives 4, term 2 gives 7, term 3 gives 10. I will send the next term-numbers through the machine and build a two-row table on the board as the values land, while you watch and call out each value. Then we will agree on the rule in words together.

    Find the rule: 4, 7, 10

    4 - Build the Table in Your Copy ~3 mins

    COPYBOOK MOMENT

    Illustration for Build the Table in Your CopyIn your maths copy, draw a two-row table with the top row labelled term-number and the bottom row labelled value. Fill in terms 1 to 5 for our pattern, then write the rule as a sentence underneath the table.

    5 - Class Challenge ~8 mins

    Today we crack the rule for a few of these patterns by sending term-numbers through the machine and watching the values. Once we have the rule, we will use it to leap straight to a far term, without drawing every step in between.

    Crack the hidden rule

    6 - What Did We Notice? ~3 mins

    MATHS TALK

    How does the table help us see the rule that the picture hides? Which was easier for you: reading the rule from the row of patterns, or reading it from the table of numbers?

    7 - What's Next ~3 mins

    What we learned

    • A two-row table of term-number against value lays a pattern out so its rule is easy to spot.
    • The step between values tells you the number to multiply the term by; the rest of the rule is the adjustment that sets where the pattern starts.
    • Once you have the rule in words, you can leap straight to any term without drawing every step.

    Coming up

    Coming up

    Next we look at the properties of operations and the distributive law — how multiplication shares out over addition, so a tricky product becomes two easy ones.

    Pupil practice
    Module 10 · Algebra: Patterns, Expressions and Equations Mixed
    Lesson 105 · Rules for Patterns Using Words and Tables
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