Students will decode a letter for George Washington by solving 8 algebra based math problems stressing the importance of the order of operations. Using their answers and the Culper Code, a spy code used during the American Revolution, students will fill in the blanks of Culper Spy Ring member Caleb Brewster’s 1781 letter to George Washington.

1. Getting Started
The Culper Spy Ring was organized in 1778 to collect information about British troops near
New York City. Major Benjamin Tallmadge was put in charge of the spy network and created a
special code book used by members of the spy ring to send and receive messages.
The Culper Code Book substituted seven hundred and sixty-three words, names, and places
with numbers. For instance, the number 711 denoted George Washington while 522 was used to
refer to Parliament. Benjamin Tallmadge made allowances for words not included in the code
by providing a substitution for the twenty-six letters of the alphabet and single digit numbers 0
though 9.
Help decode a letter for George Washington!
Caleb Brewster, a member of the Culper Spy Ring known as Agent 725, wrote a letter to
George Washington on July 30, 1781. In this letter, he reported the newest intelligence about
the movement of British Troops in the New York area.
The Education Department at George Washington’s Mount Vernon has removed eight key
words from an excerpt of Brewster’s letter to George Washington and challenges your students
to fill in the blanks. After solving each math problem on the following page, instruct students to
find their answers in the Culper Code Book to determine the missing words from the letter to
George Washington.
Discussion Prompts
Students can read Caleb Brewster’s full letter to George Washington dated July 31,
1781 on the Founders Online website.
Use the following questions to help students connect Caleb Brewster’s letter to the
larger story of the American Revolution.
1. When did Caleb Brewster write his letter to George Washington?
2. Where was Brewster when he wrote his letter to George Washington? Locate this
place on a map.
3. Where was Admiral Graves taking Lord Cornwallis and his troops?
4. Why do you think General George Washington would be interested in knowing
where the British troops were moving to?
5. How do you think George Washington might have used this information to his
benefit?
Decipher the Culper Code
High School Algebra

2. To decode the message: Solve the following math problems for “z” paying particular
attention to the order of operations. Use the Culper Code provided by your teacher to find
the words that match your answers. Fill in the missing words to find out what message
Caleb Brewster wrote to George Washington on July 30, 1781.
Decipher the Culper Code
1.
z ÷ 4 = (8x4) + 3(200 ÷ 4)
WORD:
Sir, Fairfield, July 30th 1781
This day I arrived from ___________________ the latest Intelligence I could ___________________
1. 2.
was Friday ___________________ - Of the Sailing of Admiral Graves from Sandy Hook for
3.
___________________ , for the ___________________ of Conveying ___________________
4. 5. 6.
Cornwallis, with his ___________________ & Army at ___________________...
7. 8.
...I am sir, with the Greatest Respect Your Excellency’s Most Obedt Humble Servant
Caleb Brewster
2.
z = 2(112
) - (3x7)
2
WORD:
3.
(23
+62
)2
= (z x 6) - (32
(18+2) - 2)
WORD:
4.
(z-32
) = (52x4) + (20x26.5) - 8
WORD:
5.
6(√144 + 53
) = z + 2(122
) + (-7)2
WORD:
6.
(54
- 132
)= (z + 72
) - (70 x 4 ) - 6
4
WORD:
7.
(8 x -4) + z + 82
= (√81 + √36)2
WORD:
8.
(33
)2
- 2 = z
WORD:

3. To decode the message: Solve the following math problems for “z” paying particular
attention to the order of operations. Use the Culper Code provided by your teacher to find
the words that match your answers. Fill in the missing words to find out what message
Caleb Brewster wrote to George Washington on July 30, 1781.
Decipher the Culper Code
Sir, Fairfield, July 30th 1781
This day I arrived from ____Long Island___ the latest Intelligence I could _______obtain______
1. 2.
was Friday _______last________ - Of the Sailing of Admiral Graves from Sandy Hook for
3.
______ Virginia__ ___ , for the ____ __purpose__ ___ of Conveying ________Lord______
4. 5. 6.
Cornwallis, with his ______ fleet______ & Army at __ _New York_____...
7. 8.
...I am sir, with the Greatest Respect Your Excellency’s Most Obedt Humble Servant
Caleb Brewster
3.
(23
+62
)2
= (z x 6) - (32
(18+2) - 2)
z = 353
WORD: last
4.
(z-32
) = (52x4) + (20x26.5) - 8
z = 739
WORD: Virginia
5.
6(√144 + 53
) = z + 2(122
) + (-7)2
z = 485
WORD: purpose
6.
(54
- 132
)= (z + 72
) - (70 x 4 ) - 6
4
z = 351
WORD: Lord
7.
(8 x -4) + z + 82
= (√81 + √36)2
z = 193
WORD: fleet
8.
(33
)2
- 2 = z
z = 727
WORD: New York
Answer Key
1.
z ÷ 4 = (8x4) + 3(200 ÷ 4)
z = 728
WORD: Long Island
2.
z = 2(112
) - (3x7)
2
z = 442
WORD: obtain