Vault Cracker Practice Worksheet
Codebreaker Math Double Regrouping
VAULT CRACKER SUBTRACTION
Target Range 500 – 999
Agent Name:
Date:
Score: / 20
Vault Decoding Protocol (Double Regrouping)
1. Ones Dial If top digit < bottom digit, borrow 1 ten (\(10\text{ ones}\)). Add to ones.
2. Tens Dial If remaining tens < bottom tens, borrow 1 hundred (\(10\text{ tens}\)).
3. Hundreds Dial Subtract the remaining hundreds digits to crack the final combination code!
1 Guided Dial Calibration (Use the regrouping scratch boxes)
Regroup both tens and ones
LOCK #1 H T O
7 2 4
− 3 5 8
LOCK #2 H T O
8 3 1
− 4 7 5
LOCK #3 H T O
9 1 5
− 5 6 9
LOCK #4 H T O
6 4 2
− 2 8 7
2 High-Security Vault Chamber (Full Regrouping)
Show all borrow lines clearly
VAULT 05 Regroup 10s & 100s
7 5 3
− 4 8 6
VAULT 06 Regroup 10s & 100s
9 3 4
− 5 7 8
VAULT 07 Regroup 10s & 100s
8 6 2
− 3 9 7
VAULT 08 Regroup 10s & 100s
5 2 1
− 2 8 6
VAULT 09 Regroup 10s & 100s
9 4 5
− 6 7 9
VAULT 10 Regroup 10s & 100s
8 1 6
− 4 5 8
Vault Cracker Subtraction • Section 1 of 2 Turn to Page 2 for The Zero Zone & Word Missions →
2
VAULT CRACKER • PHASE II: ZERO ZONE & FIELD MISSIONS
Agent: ___________________
3
The Zero Zone: Regrouping Across Zeros
Rule: Borrow from the hundreds first to turn 0 tens into 10 tens!
LOCK #11
8 0 0
− 3 6 4
LOCK #12
7 0 4
− 2 5 8
LOCK #13
9 0 0
− 5 4 7
LOCK #14
6 0 3
− 3 7 9
4
Mission Dispatch: Real-World Math Operations
MISSION #15:
Agent Cipher must decrypt a bank firewall with 825 encrypted security layers. By midnight, she successfully cracks 468 layers. How many encrypted layers still remain to be decrypted?
Number Sentence:
Vertical Calculation:
Final Answer with Units:
MISSION #16:
A high-security treasury started the morning with 950 gold tokens. An armored vehicle safely transported 674 tokens to a secure vault across town. How many gold tokens are still inside the treasury?
Number Sentence:
Vertical Calculation:
Final Answer with Units:
5
Security Breach: Error Analysis Challenge
Flawed Attempt
7 1 3
− 3 8 9
4 7 6
"The rogue agent subtracted smaller digits from larger digits upside down without regrouping!"
Explain the agent's exact mistake:
Correct Code:
Vault Cracker Subtraction • Section 2 of 2 Code Mastered: 3-Digit Double Regrouping
Vault Cracker Answer Key
Teacher Reference Step-by-Step Key
VAULT CRACKER ANSWER KEY
Double Regrouping Solutions
Key Instructional Watch-Fors & Diagnostics
Top-from-bottom inversion: Students struggling with 3-digit subtraction often subtract smaller from larger (\(8 - 4 = 4\) instead of regrouping). Check that students cross out the minuend digits before subtracting and properly reflect the decreased values (\(7 \to 6\), \(2 \to 1 \to 11\)).
1 Guided Dial Calibration Solutions (Problems 1–4)
Complete Borrowing Steps Shown
LOCK #1 H T O
6 11 14
7 2 4
− 3 5 8
3 6 6
LOCK #2 H T O
7 12 11
8 3 1
− 4 7 5
3 5 6
LOCK #3 H T O
8 10 15
9 1 5
− 5 6 9
3 4 6
LOCK #4 H T O
5 13 12
6 4 2
− 2 8 7
3 5 5
2 Vault Chamber Solutions (Problems 5–10)
Includes intermediate regrouping breakdown
VAULT 05 753 → 6 H, 14 T, 13 O
6 14 13
7 5 3
− 4 8 6
2 6 7
VAULT 06 934 → 8 H, 12 T, 14 O
8 12 14
9 3 4
− 5 7 8
3 5 6
VAULT 07 862 → 7 H, 15 T, 12 O
7 15 12
8 6 2
− 3 9 7
4 6 5
VAULT 08 521 → 4 H, 11 T, 11 O
4 11 11
5 2 1
− 2 8 6
2 3 5
VAULT 09 945 → 8 H, 13 T, 15 O
8 13 15
9 4 5
− 6 7 9
2 6 6
VAULT 10 816 → 7 H, 10 T, 16 O
7 10 16
8 1 6
− 4 5 8
3 5 8
Teacher Answer Key • Page 1 of 2 See Page 2 for Zero Zone, Word Problems, and Error Analysis keys
2
VAULT CRACKER KEY • ZERO ZONE & FIELD MISSIONS
Phase II Official Solutions
3
The Zero Zone Solutions (Regrouping Across Zeros)
Chain Borrowing Pathway
LOCK #11 7 | 9 | 10
8 0 0
− 3 6 4
4 3 6
\(8\text{H} \to 7\text{H}, 10\text{T} \to 9\text{T}, 10\text{O}\)
