Finding the Fourth Proportional to 82.16, 122.56 and 78.72

Step by Step Solution

1. Step 1: Write the proportion equation
   82.16 : 122.56 = 78.72 : x
2. Step 2: Convert to fraction form
   82.16/122.56 = 78.72/x
3. Step 3: Cross multiply
   82.16x = 122.56 × 78.72
4. Step 4: Simplify right side
   82.16x = 9,647.92
5. Step 5: Solve for x
   x = 9,647.92/82.16
6. Step 6: Final answer
   x = 117.43