Mathematics, Algebra and Function
Grade 5 8
Objective
Students use codes to learn prealgebra concepts.
Directions
Facts and Reminders
Simple Codes
This is a simple code because 43 + 32 = 75.
Using Reverse Operations
In the problem below, to crack the code you must subtract 98 from 123. The answer is 25.
Problem 
Step 
Check 
Solution 
98 

98 
+ DF 
123  98 = 25 
+ 25 
D = 2 
F = 5 
123 

123 
In this next problem, to crack the code, you must divide 1,428 by 42. The answer is 34.
Problem 
Step 
Check 
Solution 
42 

42 
x AF 

x 34 
168 
1428 ÷ 42 = 34 
168 
A = 3 
F = 4 
1260 

1260 
1428 

1428 
Using Number Sense
In the problem below, you can try two ways to crack the code. One way is to try each digit 1 through 9. Another way is knowing that 6 = 2 x 3 and trying 2 first.
Problem 
Check 
Solution 
31 
31 
x AA 
x 22 
6A 
62 
A = 2 
6A0 
620 
68A 
682 
In the next problem, you know that the only number that added to itself and equals 2 is 1.
Problem 
Check 
Solution 
BBB 
111 
+ BBB 
+ 111 
B = 1 
2 2 2 
222 
In the problem below, ask yourself the question, "Which number times itself equals 9?" The answer is 3.
Problem 
Check 
Solution 
FFF 
333 
x F 
x 3 
F = 3 
999 
999 
Resources
 Code Cracking activity sheet
 pencils