Finding the Fourth Proportional to 91.86, 126.82 and 78.78

Step by Step Solution

1. Step 1: Write the proportion equation
   91.86 : 126.82 = 78.78 : x
2. Step 2: Convert to fraction form
   91.86/126.82 = 78.78/x
3. Step 3: Cross multiply
   91.86x = 126.82 × 78.78
4. Step 4: Simplify right side
   91.86x = 9,990.88
5. Step 5: Solve for x
   x = 9,990.88/91.86
6. Step 6: Final answer
   x = 108.76