Finding the Fourth Proportional to 85.82, 128.73 and 20.82

Step by Step Solution

1. Step 1: Write the proportion equation
   85.82 : 128.73 = 20.82 : x
2. Step 2: Convert to fraction form
   85.82/128.73 = 20.82/x
3. Step 3: Cross multiply
   85.82x = 128.73 × 20.82
4. Step 4: Simplify right side
   85.82x = 2,679.64
5. Step 5: Solve for x
   x = 2,679.64/85.82
6. Step 6: Final answer
   x = 31.23