Math · Stage 2

Pick to be sure: the worst case with larger sets

More kinds, same clever idea — plan for the unluckiest grab, then one more guarantees a matching pair.

✦ Math📘 Stage 2 · S2⏱ ~10 min🧒 Ages 6–7★ Free to start

I can find how many to pick to be sure (worst case) with larger sets.

📖

Kavi's Big Button Jar 🫙

Kavi's giant jar holds buttons in 6 colours — all mixed up, and it's too dark to peek! "How many buttons must I scoop to be SURE two match?" Kavi pictures the unluckiest scoop: one of every colour — 6 buttons, still no pair! But the very next button must repeat a colour. So 6 colours + 1 = 7 buttons are guaranteed. More kinds? Same clever rule: just add 1!

🎓

What your child will learn

1Lucky grab vs sure grabTo be SURE you must plan for the unluckiest grab, never the luckiest. Tap each card and see the difference with a big jar of 6 colours.

2The unluckiest scoop, bigger jarImagine the unluckiest scoop from a 4-colour jar: one of each colour first — 4 buttons, still no pair! Sort these five buttons into colour bins and watch the 5th button: it must repeat a colour and make a pair.

3The rule scales: kinds + 1Write it as a number bond. However big the set, the socks/buttons you need is the number of kinds plus 1. For 6 colours: 6 + 1 = 7.

🔍

A peek inside

A jar has buttons in 4 colours. How many must Kavi scoop in the dark to be SURE two match?

worst case = one of each colour = 4 buttons, no pair yet · the next must repeat → 4 + 1

Try this at home: Buttons come in 4 colours in a dark jar. How many must you scoop to be sure of a matching pair? Why?

Ready to play and learn?

Start the free interactive lesson, or print the handout for screen-free play.

Start the free lesson →⬇ Download PDF

Part of Math · Stage 2 · S2 on KAVI Academy — a secular, whole-child learning platform for ages 5–12.