Pin Down a Number from Digit and Range Conditions
A hidden number is found by applying clues in turn — digit constraints, place-by-place comparison, and inequality bounds that fence the unknown into a finite range. Early versions narrow a four-digit number from digit clues; later versions bound an unknown digit or an unknown box value under a sum, product, or comparison constraint. The shared move is converting each condition into a restriction until one survivor remains.
grade 2–4 Base-ten numbersOperations Eliminate PossibilitiesMake a Systematic List
Progression (9)
g4 1. Compare numbers with an unknown digit Base-ten numbers
g4 2. Find a number from digit clues Base-ten numbers
g3 3. Bound an inequality at equality Operations
g3 4. Find a number satisfying product bounds Operations
g3 5. Bigger addend, bigger sum OperationsBase-ten numbers
g3 6. Estimate a product to solve an inequality Base-ten numbersOperations
g3 7. Estimate a product to bound an unknown Base-ten numbersOperations
g4 8. Build a number from digit conditions in order Base-ten numbers
g4 9. Compare place by place to bound an unknown digit Base-ten numbers
Bridges to competition (16)
Reasoning problems that extend this idea toward competition:
Build an equation meeting given conditions Number arrangement
Numbers with swapped digit places Number arrangement
Number satisfying sum and product clues Number arrangement
Complete an arithmetic placement puzzle Number arrangement
Find unknowns satisfying multiple conditions Logic
Find fractions meeting conditions Logic
Find a Number Meeting Digit Conditions Number arrangement
Deduce the hidden flipped cards Logic
Numbers satisfying several conditions Number arrangement
Insert plus and minus to make an equation Logic
Arrange digit cards to hit a target number Number arrangement
Insert plus or minus to make an equation true Number arrangement
Deduce digits and place values from clues Logic
Ascending, descending, palindrome numbers Number arrangement
Find numbers meeting digit clues Logic
Find a number meeting given conditions Number arrangement