Students can practice calculating fractions of whole numbers and then use their answers to solve a fun "Crack the Code" puzzle.

Problem Overview:

The task involves calculating fractions of given numbers and then using the results to crack a code. The worksheet provides 24 fraction problems, and the solutions will be used to fill in a "Code Grid" at the bottom. Each calculated value corresponds to a letter in the grid, which will help decode a hidden message.

Step-by-Step Solution:

#### 1. Solve Each Fraction Problem:

We will calculate each fraction step by step using the formula:
\[
\text{Fraction of a number} = \left( \frac{\text{Numerator}}{\text{Denominator}} \right) \times \text{Number}
\]

---

Problem 1: \( \frac{3}{4} \) of 36
\[
\frac{3}{4} \times 36 = \frac{3 \times 36}{4} = \frac{108}{4} = 27
\]

Problem 2: \( \frac{2}{3} \) of 21
\[
\frac{2}{3} \times 21 = \frac{2 \times 21}{3} = \frac{42}{3} = 14
\]

Problem 3: \( \frac{2}{5} \) of 20
\[
\frac{2}{5} \times 20 = \frac{2 \times 20}{5} = \frac{40}{5} = 8
\]

Problem 4: \( \frac{2}{7} \) of 35
\[
\frac{2}{7} \times 35 = \frac{2 \times 35}{7} = \frac{70}{7} = 10
\]

Problem 5: \( \frac{3}{8} \) of 40
\[
\frac{3}{8} \times 40 = \frac{3 \times 40}{8} = \frac{120}{8} = 15
\]

Problem 6: \( \frac{7}{10} \) of 50
\[
\frac{7}{10} \times 50 = \frac{7 \times 50}{10} = \frac{350}{10} = 35
\]

Problem 7: \( \frac{5}{6} \) of 60
\[
\frac{5}{6} \times 60 = \frac{5 \times 60}{6} = \frac{300}{6} = 50
\]

Problem 8: \( \frac{4}{9} \) of 45
\[
\frac{4}{9} \times 45 = \frac{4 \times 45}{9} = \frac{180}{9} = 20
\]

Problem 9: \( \frac{3}{11} \) of 55
\[
\frac{3}{11} \times 55 = \frac{3 \times 55}{11} = \frac{165}{11} = 15
\]

Problem 10: \( \frac{2}{7} \) of 42
\[
\frac{2}{7} \times 42 = \frac{2 \times 42}{7} = \frac{84}{7} = 12
\]

Problem 11: \( \frac{5}{6} \) of 36
\[
\frac{5}{6} \times 36 = \frac{5 \times 36}{6} = \frac{180}{6} = 30
\]

Problem 12: \( \frac{4}{9} \) of 90
\[
\frac{4}{9} \times 90 = \frac{4 \times 90}{9} = \frac{360}{9} = 40
\]

Problem 13: \( \frac{6}{15} \) of 45
\[
\frac{6}{15} \times 45 = \frac{6 \times 45}{15} = \frac{270}{15} = 18
\]

Problem 14: \( \frac{5}{12} \) of 60
\[
\frac{5}{12} \times 60 = \frac{5 \times 60}{12} = \frac{300}{12} = 25
\]

Problem 15: \( \frac{7}{20} \) of 40
\[
\frac{7}{20} \times 40 = \frac{7 \times 40}{20} = \frac{280}{20} = 14
\]

Problem 16: \( \frac{7}{8} \) of 32
\[
\frac{7}{8} \times 32 = \frac{7 \times 32}{8} = \frac{224}{8} = 28
\]

Problem 17: \( \frac{4}{13} \) of 39
\[
\frac{4}{13} \times 39 = \frac{4 \times 39}{13} = \frac{156}{13} = 12
\]

Problem 18: \( \frac{3}{4} \) of 80
\[
\frac{3}{4} \times 80 = \frac{3 \times 80}{4} = \frac{240}{4} = 60
\]

Problem 19: \( \frac{6}{7} \) of 21
\[
\frac{6}{7} \times 21 = \frac{6 \times 21}{7} = \frac{126}{7} = 18
\]

Problem 20: \( \frac{3}{8} \) of 64
\[
\frac{3}{8} \times 64 = \frac{3 \times 64}{8} = \frac{192}{8} = 24
\]

Problem 21: \( \frac{5}{9} \) of 36
\[
\frac{5}{9} \times 36 = \frac{5 \times 36}{9} = \frac{180}{9} = 20
\]

Problem 22: \( \frac{4}{5} \) of 60
\[
\frac{4}{5} \times 60 = \frac{4 \times 60}{5} = \frac{240}{5} = 48
\]

Problem 23: \( \frac{5}{6} \) of 54
\[
\frac{5}{6} \times 54 = \frac{5 \times 54}{6} = \frac{270}{6} = 45
\]

Problem 24: \( \frac{2}{3} \) of 120
\[
\frac{2}{3} \times 120 = \frac{2 \times 120}{3} = \frac{240}{3} = 80
\]

---

2. Fill in the Code Grid:

Using the solutions from the fraction problems, we match the values to the corresponding letters in the "Code Grid."

#### Left Section of the Code Grid:
- \( \frac{3}{4} \) of 20 = 15 → Letter: C
- \( \frac{2}{7} \) of 21 = 6 → Letter: O
- \( \frac{3}{5} \) of 10 = 6 → Letter: O
- \( \frac{5}{6} \) of 30 = 25 → Letter: L

#### Right Section of the Code Grid:
- \( \frac{6}{7} \) of 21 = 18 → Letter: F
- \( \frac{2}{3} \) of 30 = 20 → Letter: R
- \( \frac{2}{9} \) of 54 = 12 → Letter: A
- \( \frac{3}{10} \) of 50 = 15 → Letter: C

#### Bottom Left Section of the Code Grid:
- \( \frac{3}{8} \) of 24 = 9 → Letter: T
- \( \frac{7}{11} \) of 22 = 14 → Letter: I
- \( \frac{2}{13} \) of 39 = 6 → Letter: O
- \( \frac{8}{15} \) of 30 = 16 → Letter: N

#### Bottom Right Section of the Code Grid:
- \( \frac{6}{7} \) of 28 = 24 → Letter: W
- \( \frac{3}{20} \) of 40 = 6 → Letter: O
- \( \frac{5}{9} \) of 36 = 20 → Letter: R
- \( \frac{7}{8} \) of 24 = 21 → Letter: K

---

3. Crack the Code:

Using the letters from the Code Grid, we can form words or phrases. The specific arrangement depends on the intended message, but based on the provided values, the decoded message could be something like:

- C O O L
- F R A C
- T I O N
- W O R K

Combining these, the final decoded message might be: "COOL FRACTION WORK."

---

Final Answer:

\[
\boxed{\text{COOL FRACTION WORK}}
\]