Reasoning · Grade 2-1 Calculating to Meet Conditions
Problem
The ones must end in 5, and only 9 + 6 = 15 does.
Looking only at the ones column is a smaller, easier question that fixes half the puzzle in one step — a Grade 2 'which digits land in the ones place?' idea.
2.NBT.A.1Solve An Easier Related ProblemLooking only at the ones column decides which two cards are the ones digits before anything else is settled.
Only the ones digits of the two numbers reach the ones place of the answer, so that column can be judged without knowing the tens.
Only a few card pairs can make the required ones digit at all, and every other pair is crossed out on the spot.
That leaves 7 and 2 on top; with the carry, 90 + 15 = 105.
Adding the tens and the carry is exactly the place-value addition Grade 2 learners practice within 100.
2.NBT.B.5Draw A DiagramListing the arrangements: 79 + 26, 76 + 29, 26 + 79, 29 + 76.
Once the column digits are fixed, simply listing the orderings catches every case without missing or repeating any.
2.OA.B.2Make A Systematic ListFor (2), testing the splits leaves only 54 − 38 = 16.
Trying each digit-pairing and subtracting within 100 is a quick guess-and-check a Grade 2 student can do by hand.
2.NBT.B.5Guess And CheckRegrouping gives 14 − 8 = 6 and 4 − 3 = 1, so the answer is unique.
Re-doing the subtraction with regrouping confirms the answer and shows the place-value carry the way Grade 2 checks subtraction within 100.
2.OA.B.2Make A Systematic ListLook at the ones column first — it tells you which digits go where, and then the rest of the puzzle is just Grade 2 adding and subtracting within 100!