Problem 7 Solution Ans: 335
H T O
new
7
12
5 8 2
− 2 4 7
3
3
5
Problem 8 Solution Ans: 355
H T O
new
5
12
6 2 8
− 2 7 3
3
5
5
Problem 9 Solution Ans: 564
H T O
new
7
13
13
8 4 3
− 2 7 9
5
6
4
Problem 10 Solution Ans: 467
H T O
new
8
12
15
9 3 5
− 4 6 8
4
6
7
Problem 11 Solution Ans: 358
H T O
new
6
10
14
7 1 4
− 3 5 6
3
5
8
Problem 12 Solution Ans: 232
H T O
new
7
11
11
8 2 1
− 5 8 9
2
3
2
Checking Rule: Difference + Subtrahend = Minuend (e.g. 232 + 589 = 821) Page 2 Master Key • 6 Points Total
Answer Key Part 3: Across Zeroes Mastery
TEACHER REFERENCE GUIDE
Full Solutions & Chain Unbundling (Problems 13–18)
Chain Unbundling intermediate values shown
TEACHING TIP
The Conceptual Reason for 9: In whole hundreds (e.g. 600 − 374), explain that 600 unbundles into 5 hundreds and 10 tens. Then 1 ten unbundles to make 10 ones, leaving 9 tens in the middle.
Problem 13 Solution Ans: 268
H T O
step
4
9
16
5 0 6
− 2 3 8
2
6
8
Problem 14 Solution Ans: 346
H T O
step
7
9
13
8 0 3
− 4 5 7
3
4
6
Problem 15 Solution Ans: 354
H T O
step
6
9
10
7 0 0
− 3 4 6
3
5
4
Problem 16 Solution Ans: 318
H T O
step
8
9
10
9 0 0
− 5 8 2
3
1
8
Problem 17 Solution Ans: 226
H T O
step
5
9
10
6 0 0
− 3 7 4
2
2
6
Problem 18 Solution Ans: 365
H T O
step
7
9
12
8 0 2
− 4 3 7
3
6
5
Part 3 Key • 6 Points Total Turn page for Early Finisher Champion Round Key
Answer Key Part 4: Early Finisher Champion Round
TEACHER REFERENCE GUIDE
Champion Round Solutions & Advanced Regrouping Tracking (Problems 19–24)
Three-Digit Mastery worked solutions
TEACHING TIP
Pedagogical Note for Problems 19 & 21: In 923 − 487 and 904 − 568, students practice consecutive unbundling without exceeding 3 digits. Ensure they write the intermediate decomposed values cleanly in the top boxes.
Problem 19 Solution Ans: 436
H T O
new
8
11
13
9 2 3
− 4 8 7
4
3
6
Problem 20 Solution Ans: 1,641
Th H T O
1
1
1
9 8 7
1
6
4
1
Problem 21 Solution Ans: 336
H T O
step
8
9
14
9 0 4
− 5 6 8
3
3
6
Problem 22 Solution Ans: 1,665
Th H T O
1
1
1
8 7 6
1
6
6
5
Problem 23 Solution Ans: 424
H T O
step
8
9
12
9 0 2
− 4 7 8
4
2
4
Problem 24 Solution Ans: 333
H T O
step
7
9
10
8 0 0
− 4 6 7
3
3
3
Packet Total: 24 Questions (Pure Three-Digit Addition & Subtraction Challenges) Complete Key • 24 Points Total (100%)
H T O
new
4 9 0
− 1 6 3
Notice: Notice how only the tens are unbundled—the hundreds digits subtract without borrowing!
Score: ____ / 6
Mixed Review Addition & Subtraction
Name:
Date:
Part 3: Mixed Operations • Watch the Signs (+ vs −) in the Tens Column!
+ Carry in Tens − Borrow from Tens
! Sign Alert: Check the operation sign first! If (+), carry 1 ten over to the hundreds. If (−), borrow 1 ten to help the ones column!
Problem 13 Addition • Carry Tens
H T O
step
3 9 2
Problem 14 Subtract • Borrow Tens
H T O
step
7 8 1
− 4 3 6
Problem 15 Addition • Carry Tens
H T O
step
5 8 4
Problem 16 Subtract • Borrow Tens
H T O
step
6 7 5
− 2 2 8
Problem 17 Addition • Carry Tens
H T O
step
4 6 3
Problem 18 Subtract • Borrow Tens
H T O
step
8 9 4
− 3 6 7
Tens Mastery Complete! You mastered isolated carrying and borrowing in the tens place!
Overall Score: ____ / 18
13
6 8 3
− 2 4 7
4
3
6
Problem 8 Solution Ans: 434
H T O
new
8
12
7 9 2
− 3 5 8
4
3
4
Problem 9 Solution Ans: 335
H T O
new
6
14
5 7 4
− 2 3 9
3
3
5
Problem 10 Solution Ans: 436
H T O
new
5
11
8 6 1
− 4 2 5
4
3
6
Problem 11 Solution Ans: 437
H T O
new
7
15
9 8 5
− 5 4 8
4
3
7
Problem 12 Solution Ans: 327
H T O
new
8
10
4 9 0
− 1 6 3
3
2
7
Tens Subtraction Standard: CCSS.MATH.CONTENT.3.NBT.A.2 Page 2 Master Key • 6 Points
Answer Key Mixed Tens Focus
TEACHER REFERENCE GUIDE
Part 3: Mixed Operations • Discrimination Solutions (Problems 13–18)
Full Worked Solutions shown
TEACHING TIP
Sign Discrimination: When switching rapidly between addition and subtraction, students frequently borrow during addition or carry during subtraction. Use this page to diagnose sign confusion.
Problem 13 Solution (+) Ans: 637
H T O
step
1
3 9 2
6
3
7
Problem 14 Solution (−) Ans: 345
H T O
step
7
11
7 8 1
− 4 3 6
3
4
5
Problem 15 Solution (+) Ans: 756
H T O
step
1
5 8 4
7
5
6
Problem 16 Solution (−) Ans: 447
H T O
step
6
15
6 7 5
− 2 2 8
4
4
7
Problem 17 Solution (+) Ans: 844
H T O
step
1
4 6 3
8
4
4
Problem 18 Solution (−) Ans: 527
H T O
step
8
14
8 9 4
− 3 6 7
5
2
7
Tens Mastery Key Complete: 18 Questions (6 Addition + 6 Subtraction + 6 Mixed) Total Score: 18 / 18 (100%)
