Here are five hurling match crowds from last summer, all jumbled up on the board: 1,200, then 980, then 1,020, then 875, then 1,105.

If you had to line them up from the smallest crowd to the biggest, where would you start? Which one jumps out at you as the smallest of all?

Each set of numbers is shown already sorted from smallest to biggest. Watch which column decides the order, start at the thousands and only move right when they tie.

Now we order some sets together on the board, one at a time. We work through three sets in turn: first {720, 1,050, 950}, then {5,600, 5,060, 5,006}, then {4,180, 4,081, 4,810, 4,018}. Each set is a little trickier than the last — the last one has four numbers whose digits shuffle around, so we read right to the units before we decide.

Each time, a different pupil comes to the board and drags the smallest number that is left, then the next smallest, until the whole set is lined up from least to greatest. The rest of us say aloud which column decided each choice.

Time for the challenge sets. We work through these in order, each a step harder: {850, 1,005, 990}, then {3,400, 3,040, 3,004}, then {7,210, 7,021, 7,201, 7,012}, and finally {9,090, 9,009, 9,900, 9,000}. That last one is the one that catches people out — every number is nines and zeros, so you have to read right along before you can decide.