Finding the Fourth Proportional to 81.72, 113.06 and 78.72

Step by Step Solution

1. Step 1: Write the proportion equation
   81.72 : 113.06 = 78.72 : x
2. Step 2: Convert to fraction form
   81.72/113.06 = 78.72/x
3. Step 3: Cross multiply
   81.72x = 113.06 × 78.72
4. Step 4: Simplify right side
   81.72x = 8,900.08
5. Step 5: Solve for x
   x = 8,900.08/81.72
6. Step 6: Final answer
   x = 108.91