Unit 7 · Finding Procedures
Connor at the Fair — Work Backwards to Find the Start
Lesson 1 of 4
Fair-money puzzles are working backwards: start from what is left and undo each spend in reverse order until you reach the starting amount.
Half-then-fixed-spend items appear in the easy band of Selective MR — reliable marks when you reverse the steps instead of guessing from the options.
The examiner checks whether you can undo sequential operations (halving, subtracting a fixed amount) to recover the original value.
Someone spends half their money, then a fixed dollar amount, and has a stated amount left. You find how much they started with.
Best approach: After the fixed spend they had (left + fixed). Before halving they had double that. Check forward: half, subtract, equals the given remainder.
Question
Connor goes to the fair.
- He spends half his money on rides.
- He then spends $4 on food.
- He has $6 left.
How much money did Connor start with?
Select an answer to see the explanation.
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