1
4 7
72
512
6 2
− 3 8
24
1
5 6
95
714
8 4
− 2 7
57
1
3 8
82
611
7 1
− 4 5
26
1
6 9
92
810
9 0
− 5 4
36
1
5 8
85
413
5 3
− 2 9
24
1
4 9
85
715
8 5
− 4 7
38
13. Library: 48 books + 37 books.
\(48 + 37 = 85\) (carry 1 ten)
Answer: 85 books
14. Sports Shop: 75 soccer balls − 38 sold.
\(75 - 38 = 37\) (borrow 1 ten)
Answer: 37 balls
Number Crunchers Teacher Guide Page 2 Solutions
Teacher Key
Answer Key • Independent Practice 3: Regrouping Power & Error Detective
Key Page 3 of 8
Total Problems: 10 Items Grid: 8 pts • Error Sleuth Cases: 4 pts (2 pts each)
1
7 8
143
813
9 3
− 4 6
47
1
8 6
143
711
8 1
− 3 7
44
1
9 4
172
610
7 0
− 2 6
44
1
5 9
142
514
6 4
− 2 8
36
Case #1 Analysis: Leo's Subtraction
Error: Leo subtracted \(8 - 4 = 4\) instead of borrowing from the tens.
Fix: Cross out 5, write 4 tens; change 4 to 14 ones. \(14 - 8 = 6\), \(4 - 2 = 2\).
Correct Computation: 54 − 28 = 26
Correct Answer: 26
Case #2 Analysis: Sara's Addition
Error: Sara did \(7 + 5 = 12\), but forgot to carry 1 ten to the tens column.
Fix: Write 2 in ones, carry 1 ten. \(1 + 6 + 2 = 9\) tens.
Correct Computation: 67 + 25 = 92
Correct Answer: 92
Number Crunchers Teacher Guide Page 3 Solutions
Teacher Key
Answer Key • Independent Practice 4: Three-Digit Mixed Operations
Key Page 4 of 8
Total Problems: 10 Items Grid: 6 pts • Estimation Table: 3 pts • Story Problem: 1 pt
11
3 4 8
623
51412
6 5 2
− 2 8 7
365
11
4 8 9
853
61313
7 4 3
− 3 6 8
375
11
5 7 6
863
71015
8 1 5
− 4 5 9
356
| Problem | Estimate (Rounded to 100) | Exact Computation |
|---|---|---|
| 512 + 289 | 500 + 300 = 800 | 801 |
| 894 − 321 | 900 − 300 = 600 | 573 |
| 678 + 195 | 700 + 200 = 900 | 873 |
10. Food drive: 625 cans − 278 cans packed.
\(625 - 278 = 347\) (Regroup tens: 15-8=7; regroup hundreds: 11-7=4; 5-2=3)
Answer: 347 cans remaining
Number Crunchers Teacher Guide Page 4 Solutions
Teacher Key
Answer Key • Independent Practice 5: The Zero Zone & Double Regrouping
Key Page 5 of 8
Total Problems: 10 Items Grid: 6 pts • True/False: 2 pts • Digit Detective: 2 pts
4910
5 0 0
− 2 4 7
253
11
6 7 5
933
6914
7 0 4
− 3 5 9
345
8910
9 0 0
− 4 3 6
464
11
4 8 7
983
5912
6 0 2
− 2 7 8
324
7. 400 − 165 = 235
400 − 165 = 235 (Exact match)
TRUE
8. 800 − 348 = 462
800 − 348 = 452, not 462!
FALSE
5 3 3 + 248 = 781
Missing digit = 3
800 − 3 5 6 = 444
Missing digit = 5
Number Crunchers Teacher Guide Page 5 Solutions
Teacher Key
Answer Key • Independent Practice 6: Multi-Digit Mixed Showdown
Key Page 6 of 8
Total Problems: 8 Items Sprint: 6 pts • Multi-Step Problems: 4 pts (2 pts each)
9
17
16
− 7
9
74
132
92
− 46
46
467
852
703
− 284
419
7. Zoo Field Trip Worked Steps:
Step 1: Total Students \(148 + 165 = 313\) students
Step 2: Sea Lion Show \(313 - 89 = 224\) students
Reasoning: Combined classes, then subtracted the subgroup. Final Answer: 224 students
8. Community Garden Worked Steps:
Step 1: Carrots + Peppers \(184 + 159 = 343\) vegetables
Step 2: Subtract from Total \(500 - 343 = 157\) tomatoes
Reasoning: Subtracted combined sum from total harvest. Final Answer: 157 tomatoes
Number Crunchers Teacher Guide Page 6 Solutions
Teacher Key
Answer Key • Homework Page 1: Two-Digit Mixed Practice
Key Page 7 of 8
Total Homework Items: 12 Part 1: 8 pts • Part 2: 2 pts • Part 3: 2 pts (Total: 12 pts)
1
5 8
94
613
7 3
− 2 9
44
1
4 7
92
811
9 1
− 5 8
33
1
6 9
93
710
8 0
− 3 7
43
1
3 8
95
512
6 2
− 4 8
14
9. 34 + 48 = 82 TRUE
10. 71 − 26 = 55 (Actual: 45) FALSE
11. Liam: 54 pages + 39 pages.
\(54 + 39 = 93\) (4+9=13; 1+5+3=9)
Answer: 93 pages
12. Craft Store: 83 boxes − 47 boxes sold.
\(83 - 47 = 36\) (13-7=6; 7-4=3)
Answer: 36 boxes
Number Crunchers Teacher Guide Homework 1 Solutions
Teacher Key
Answer Key • Homework Page 2: Three-Digit Mixed Operations Mastery
Key Page 8 of 8
Total Homework Items: 7 Items + Reflection Grid: 6 pts • Story Problem: 1 pt • Reflection Check: Complete
11
4 6 8
843
61114
7 2 4
− 3 5 8
366
5910
6 0 0
− 2 6 7
333
11
5 8 9
835
7915
8 0 5
− 4 3 8
367
11
3 9 7
882
7. Book Fair: 850 total books − 486 sold.
\(850 - 486 = 364\) (Borrow from tens: 10-6=4; borrow from hundreds: 14-8=6; 7-4=3)
Answer: 364 books remaining
• Tier 1 (Mastery): Students demonstrating ☆☆☆ confidence and scoring 6/7+ can transition to multi-digit multiplication or 4-digit estimation challenges.
• Tier 2 (Targeted Support): For errors on subtracting across zeros (e.g. Problems 3 and 5), provide place value disks or base-ten blocks to model unbundling 100 into 10 tens, then 1 ten into 10 ones.
Number Crunchers Teacher Guide Homework 2 Solutions
