# Staircases

Purpose

In this unit students look for and describe the patterns they see in different types of staircases.

Achievement Objectives
NA2-6: Communicate and interpret simple additive strategies, using words, diagrams (pictures), and symbols.
NA2-8: Find rules for the next member in a sequential pattern.
Specific Learning Outcomes
• Continue a sequential pattern.
Description of Mathematics

In much of students’ early pattern work, the numbers involved can be compiled in tables like the one below:

 Length of garden 1 2 3 4 5 6 Number of paving stones 8 12 16 20 24 28

Two relationships can be seen:

1. The recurrence relation allows us to calculate the next number in the pattern from the previous number. In the example above the number of paving stones increases by four each time the length of the side garden is increased by one. This pattern can be seen in the second row of the table: 8, 12, 16, 20…
2. The functional relationship allows us to calculate any number in the pattern, independent of the previous number. In the example above the number of paving stones is four times the length of the garden, plus four. We can express this relationship as an equation. If P equals the number of paving stones and L equals the length of the garden, then P = 4L + 4.

In practice, recurrence relationships are easier to identify than functional ones.

Opportunities for Adaptation and Differentiation

This unit can be differentiated by varying the scaffolding of the tasks or altering the difficulty of the tasks to make the learning opportunities accessible to a range of learners. For example:

• encourage the use of physical materials as well as drawing to create patterns
• encourage students to work collaboratively with other individuals or pairs to share their discoveries
• adjust the expectations for solutions - some students may only be able to extend the pattern by one or two iterations, while others may describe a generalisation.

The materials used in this unit can be adapted to recognise diversity and student interests to encourage engagement. Instead of creating patterns with plastic classroom blocks or cubes students could be encouraged to make the patterns using environmental materials such as pebbles, shells, or daisies from the school lawn.

Required Resource Materials
• Staircase problems
• Graph paper
Activity

#### Getting Started

Today we explore up-and-down staircases to find the pattern in the number of blocks they are made from.

1. Begin the session by telling the students about up-and-down staircases:
 One block is needed to make a 1-step up-and-down staircase. It takes one step to get up and one step to get down. This is a called a 2-step staircase as it takes two steps to go up and two steps to go down.
2. Together count the steps so that the students understand why it is called a 2-step staircase.
How many blocks are in the staircase?
How many blocks do you think would be in a 3-step up-and-down staircase?
How could you work it out?
3. Give the students time to work out the number of blocks. Share the ways that they used to work it out.
4. Ask the students to guess how many cubes they think would be needed to make a 5-step staircase. Get them to build a 5-step staircase. Check their guesses.
5. Get the students to build more staircases. As they do, ask them about any patterns they see.
Some may recognise the horizontal layers as being the sequence of odd numbers. Some may see the vertical stacks.
Some may see that square numbers of blocks are always involved. This can be checked by rearranging the blocks to make square numbers (see the diagram below). This is an important discovery. Let them make it. This may require some careful scaffolding on your part.
6. Some students may wish to continue to find numbers that make larger up-and-down staircases. To keep track of the number of blocks/cubes in each staircase it might be useful to draw the staircases on graph paper. However, if the students prefer to use cubes, then they should record their results in a table.

#### Exploring

Over the next 2-3 days the students work in pairs or individually to solve the following problems. Show the students how to use grid paper to continue the patterns. As they complete the problems ask them about any patterns they see and encourage the students to record these observations with the patterns on the graph paper.

Problem 1: Straight up the stairs

How many blocks are in this 4-step-up staircase?

How many blocks would there be in a 5-step-up staircase?
How many blocks would there be in a 6-step-up staircase?
How many blocks in a 10-step-up staircase?
How many more blocks will an 11-step-up staircase need?
What is the largest up staircase that you can tell us about?

(Note: the numbers of blocks in this pattern are the triangular numbers, see Algebra Information.)

Problem 2: Climbing ladders

How many pieces of wood have we used in this 1-rung ladder?

How many pieces of wood have we used in this 2-rung ladder?

How many pieces of wood would there be in a 4-rung ladder?
How many pieces of wood would there be in a 6-rung ladder?
What is the largest ladder that you can tell us about?
How many pieces of wood will you need to add to a 7-rung ladder to get an 8-rung ladder?

(Note: the number of pieces of wood is three times the number of rungs.)

Problem 3: Small steps

Watch out! You need to take small steps to walk up and down these stairs.

 1-step 2-step 3-step

How many blocks are in the 4-step staircase?
How many blocks are in the 6-step staircase?
What is the largest staircase that you could tell us about?
Does this remind you of something you have done before?

(Note: the count here is the same as that in Problem 1.)

Problem 4: Star patterns

 This is a 1-star This is a 2-star This is a 3-star

How many blocks are in a 4-star?
How many blocks are in a 5-star?
What do you notice about the stars?
How many blocks do you need to add to a 7-star to make an 8-star?
What is the largest star that you could tell us about?

(Note: the pattern here is 1, 5, 9, 13, … At each stage you add on 4 blocks. To make a 100-star you need to have 99 lots of 4 plus one block for the centre.)

Problem 5: L-shapes

 This is a 1-L This is a 2-L This is a 3-L

How many blocks are in a 4-L?
How many blocks are in a 5-L?
What do you notice about the pattern in the L’s?
What is the largest L that you could tell us about?

(Note: to make a 100-L you need 100 + 100 – 1 = 199 blocks.)

#### Reflecting

In this session we share our solutions to the problems of the previous days. We listen carefully as the patterns are explained. We then make some block patterns of our own which we give to our classmates to continue.

1. Begin the session by asking the students to attach their solutions to the problems to a display wall. Give the students time to look at the solutions of other students. Ask for volunteers to share their solutions.
2. Give pairs of students a supply of blocks and grid paper and ask them to invent their own block pattern. Tell them to record the first three elements in the pattern on a piece of grid paper.
3. Ask the students to swap patterns with another pair. Work together to discover the pattern and then continue it.
4. Repeat with another pair’s pattern.
5. Leave the patterns on a table for the students to solve in their own time.