7+5=12; 1+8+6=15; 1+5+3=9.
14-8=6; 12-7=5; 7-4=3.
Unpack 600: 5 hundreds, 9 tens, 14 ones.
Unpack 900: 8 hundreds, 9 tens, 10 ones.
Operation Dynamo Teacher Guide Turn page for 10 Word Problem Solutions → Page 1 of 3
Full Equations, Steps, and Modeling Notes
Complete Key
#1: Maya's Seashells (2-Digit Addition) 85 seashells
Equation: \( 48 + 37 = 85 \). Regroup 15 ones into 1 ten and 5 ones; 1 + 4 + 3 = 8 tens.
#2: Bakery Muffins (2-Digit Subtraction) 28 muffins
Equation: \( 84 - 56 = 28 \). Regroup 8 tens 4 ones into 7 tens 14 ones; 14 - 6 = 8, 7 - 5 = 2.
#3: Library Cataloging (3-Digit Addition) 823 books
Equation: \( 348 + 475 = 823 \). 8 + 5 = 13 (carry 1); 1 + 4 + 7 = 12 (carry 1); 1 + 3 + 4 = 8.
#4: Food Drive Cans (3-Digit Subtraction with Regrouping) 264 cans
Equation: \( 750 - 486 = 264 \). Regroup from tens: 10 - 6 = 4. Regroup from hundreds: 14 - 8 = 6; 6 - 4 = 2.
#5: Sanctuary Tickets (Subtraction Across Zero) 173 tickets
Equation: \( 500 - 327 = 173 \). Unpack 500 into 4 hundreds, 9 tens, 10 ones: 10 - 7 = 3; 9 - 2 = 7; 4 - 3 = 1.
#6: Marcus Driving Distance (3-Digit Addition) 653 miles
Equation: \( 264 + 389 = 653 \). 4 + 9 = 13 (carry 1); 1 + 6 + 8 = 15 (carry 1); 1 + 2 + 3 = 6.
#7: Football Bleacher Seats (3-Digit Subtraction) 146 empty seats
Equation: \( 820 - 674 = 146 \). 10 - 4 = 6; regroup 8 hundreds to 7 hundreds: 11 - 7 = 4; 7 - 6 = 1.
#8: Toy Store Inventory (Two-Step Operation) 329 building sets
Step 1: \( 145 + 280 = 425 \) total sets. Step 2: \( 425 - 96 = 329 \) remaining sets.
#9: State Fair Pumpkins (Comparison Subtraction) 134 pounds heavier
Equation: \( 612 - 478 = 134 \). 12 - 8 = 4; regroup from 6 hundreds: 10 - 7 = 3; 5 - 4 = 1.
#10: Error Detective Analysis Correct Answer: 335
Diagnosis: Sofia subtracted the smaller top number from the bottom number in the ones place (\( 7 - 2 = 5 \)) and in the tens place (\( 6 - 0 = 6 \)). This is the classic "smaller from larger" misconception.
Correct Algorithm: \( 502 - 167 = 335 \). Unpack 500 to 4 hundreds, 9 tens, 12 ones: \( 12 - 7 = 5 \), \( 9 - 6 = 3 \), \( 4 - 1 = 3 \).
Operation Dynamo Teacher Guide Turn page for Exit Ticket & Misconceptions Guide → Page 2 of 3
Formative Assessment Evaluation & Intervention Strategies
Assessment & Intervention
Item 1: 2-Digit Sub
73 - 48 = 25
Regroup 7 tens to 6 tens; 13 - 8 = 5; 6 - 4 = 2.
Item 2: 3-Digit Add
468 + 375 = 843
8+5=13 (carry 1); 1+6+7=14 (carry 1); 1+4+3=8.
Item 3: Word Problem
500 - 286 = 214 miles
Regroup across zeros: 4 hundreds, 9 tens, 10 ones.
Scoring Rubric: 3/3 Correct: Ready for independent 3-digit multi-step extensions. • 2/3 Correct: Check if error was fact recall or regrouping algorithm. • 1/3 or 0/3: Pull into Tier 2 small-group manipulatives table (base-ten blocks).
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Symptoms: In \( 91 - 46 \), student writes \( 55 \) (calculates \( 6 - 1 = 5 \)).
Intervention: Use concrete base-ten blocks. Put 1 unit on the desk. Ask: "Can you give me 6 units?" Reinforce that you cannot swap places in subtraction.
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Symptoms: In \( 604 - 258 \), student tries to borrow from 0 or skips directly to hundreds without updating tens to 9.
Intervention: Teach the "Money Exchange" model. If you need dollar bills and only have a $100 bill, you must first trade for ten $10 bills, then trade one $10 bill for ten $1 bills.
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Symptoms: Adding whenever large numbers appear, ignoring keywords like "how many more", "remaining", or "left".
Intervention: Have students draw a simple Part-Part-Whole bar model before writing any digits. If they know the Whole and one Part, they must subtract to find the missing Part!
Operation Dynamo Teacher Guide Instruction Complete Page 3 of 3
