Finding the Fourth Proportional to 91.86, 137.82 and 78.12

Step by Step Solution

1. Step 1: Write the proportion equation
   91.86 : 137.82 = 78.12 : x
2. Step 2: Convert to fraction form
   91.86/137.82 = 78.12/x
3. Step 3: Cross multiply
   91.86x = 137.82 × 78.12
4. Step 4: Simplify right side
   91.86x = 10,766.50
5. Step 5: Solve for x
   x = 10,766.50/91.86
6. Step 6: Final answer
   x = 117.21