Grow all four arms
Build a later stage while conserving the original tiles.
Explore this lesson →6 practice questions · Optional read aloud · Thinking pad
Let’s understand the idea.
- Stage 1 has one center tile and one tile on each of four straight arms.
- For each next stage, add one tile to the end of every arm. Keep the existing tiles and the single center.
- At stage 6, each arm has six tiles. Count all four arms and the center once: 1 + 4 × 6 = 25.
- Opposite arms match in pairs. Their tiles have partners, leaving the center unpaired, so every stage has an odd tile count.
Something to notice
Use real tiles or paper squares to build two consecutive stages. Ask the learner to identify the four added tiles and explain why the center stays once. Invite a prediction for a later stage and an explanation of why the count stays odd. Look for equal arm lengths, no lost or duplicated tiles, and a count that includes the center. Screen practice checks a design and its count; hands-on construction and spoken reasoning provide further evidence.
Try it. Change it. Explain it.
Open the lesson to use its pictures and controls. In How it works, connect the picture to the idea. In Play & discover, change the quantities and notice what stays the same. In Your turn, answer questions and use the explanation to check your reasoning.
You can ask for help, draw on the thinking pad, or listen to the question and answer options. Progress distinguishes independent work from work completed with help.
Let’s try it →Curriculum connection
Grade 4 · 4.OA · US Common Core
This lesson is mapped to these standards. A completed activity is practice evidence, not a claim of mastery. Content is checked against the linked official standards and its mathematical models are tested.