How to do letter–number sorting tasks

Fix the rule before the run starts

The rule is stated up front. Read it first and set your piles up for it — which class reads out first, and which direction each runs. Most wrong options on these items are the correct answer to a DIFFERENT rule — the piles read out in the wrong order, one pile sorted the wrong way, the discarded class kept — and the rest are partial solves, like the run played back barely touched. A half-remembered rule walks you straight onto one of them, so before answering, re-read which rule was actually asked.

Split, sort, merge

Keep two piles — digits and letters — and slot each token into its PLACE in its pile as it arrives, so there is no sorting work left at the end. 'K 3 P 1' is held as digits 1 3, letters K P, already ordered. At the end you only read the piles out in the rule's order.

Discard means discard

Some rules use only one class — 'ignore the letters and give the numbers in increasing order'. Drop each discarded token the moment it arrives. Carrying tokens you have been told to throw away is what overruns the span, and 'the discarded class crept back in' is one of the standard wrong options.

Harder runs are flashed

On easier items the run stays on screen and re-ordering is the whole work. Harder items flash the run briefly — build the answer while it is still visible, token by token.

The strategy

1. Read the rule; say the output order to yourself.
2. Two piles; insert each token in place as it arrives.
3. Discard the ignored class instantly, if the rule names one.
4. Read out pile one, then pile two — then re-check the rule's directions.

Common traps

• Piles read out in the wrong order — letters first when numbers were asked first.
• One pile sorted the right way and the other the wrong way.
• Split done but never sorted — the tokens still in arrival order.
• The run played back untouched.
• Reversing the wrong pile on 'reverse' rules.

Worked example