A growing shape follows a rule too
A plus-shape is built from tiles. Its 4 ends are called arms. Step 1 uses 5 tiles. Step 2 adds one tile to each arm. That is 9 tiles in all.
A growing pattern changes step by step. The rule is the same every time. Add one tile to each of the 4 arms. So every step adds 4 tiles.
Step 1 has 5 tiles. Step 2 has 9. Step 3 has 13. Step 4 has 17. The count goes up by 4 at every step. 5 + 4 = 9. 9 + 4 = 13. 13 + 4 = 17.
Why this matters
Find a later step without building every step. Step 5? Add 4 to the count at step 4: 17 + 4 = 21.
Slide the step in the lab. Count the tiles.
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