Finding the Fourth Proportional to 78.61, 117.91 and 20.82

Step by Step Solution

1. Step 1: Write the proportion equation
   78.61 : 117.91 = 20.82 : x
2. Step 2: Convert to fraction form
   78.61/117.91 = 20.82/x
3. Step 3: Cross multiply
   78.61x = 117.91 × 20.82
4. Step 4: Simplify right side
   78.61x = 2,454.78
5. Step 5: Solve for x
   x = 2,454.78/78.61
6. Step 6: Final answer
   x = 31.23