Activities
Make a Number Chart
Build a 1–100 chart and circle every multiple of 7 — patterns appear instantly.
A 1–100 chart is just ten rows of ten numbers. Plain at first — until you start colouring patterns in. Then it becomes a map of the number system.
Quick check
On a 1–100 chart, you colour every multiple of 3. What shape do the coloured cells make?
Your turn
Which multiples make perfectly vertical columns on a 10-wide chart?
Colour multiples of 2, 3 and 5 and the survivors below 100 are almost all primes — that's the Sieve of Eratosthenes, done by hand.
Recap
- A 1–100 chart is 10 rows of 10.
- Multiples of divisors of 10 → straight columns.
- Other multiples → diagonal stripes.
- Crossing out small multiples reveals the primes.
Try these patterns
- Colour every multiple of 2 — you get stripes
- Colour every multiple of 5 — two clean columns
- Colour every multiple of 3 — diagonals appear
- Colour every prime — randomness with a hidden rule
Once you've coloured multiples of 2, 3 and 5, the survivors below 100 are nearly all primes. That's the Sieve of Eratosthenes — done by hand.