Problem
Reasoning · Grade 2-2 Making Four-Digit Numbers
Place the two-digit numbers using the given 453
Only one two-digit number starts with 3, so 34 and 27 fall out at once.
A two-digit number's leading digit fixes which number it can be; once one is forced, the other two-digit number has only one home left.
2.NBT.A.1Eliminate PossibilitiesOnce the leading digit forces one two-digit number into its run, the other two-digit number has only one run left to go in.
Why?
A run's first cell is its leading digit, and a number can only sit in a run whose leading digit it matches.
Why?
With one of the two runs taken and only two two-digit numbers to place, the remaining number has nowhere else to go.
Lock the three-digit runs through the 4 and the bottom 27
The down run from the 4 meeting that 2 is 402, and the middle across run is 453.
Knowing the hundreds and ones digits of a three-digit run usually pins it to exactly one of the listed numbers.
2.NBT.A.1Eliminate PossibilitiesUse the 5 to fix the first four-digit number
Just one four-digit number ends in 5, so that down run is 6715.
Matching a single known end digit against four candidates leaves just one possibility for a four-digit run.
4.NBT.A.2Eliminate PossibilitiesFinish the four-digit runs by their crossings
Crossing that 7 and a 0 fills 4070, 4630, 3069 in turn.
Each new crossing digit removes candidates until exactly one four-digit number fits each remaining run, and the shared cells all stay consistent.
4.NBT.A.2Guess And CheckFill the last three-digit runs
The leftover three-digit numbers land as 646, 536, 326, 325.
With the crossing digits known, each three-digit run has a unique match, and every shared cell agrees - the whole grid clicks into place.
2.NBT.A.1Eliminate PossibilitiesStart from the digits you already know - each fixed digit crosses out choices until only one number fits each slot!
- Place the two-digit numbers using the given 453
- Lock the three-digit runs through the 4 and the bottom 27
- Use the 5 to fix the first four-digit number
- Finish the four-digit runs by their crossings
- Fill the last three-digit runs