Finding the Fourth Proportional to 78.78, 118.17 and 78.66

Step by Step Solution

1. Step 1: Write the proportion equation
   78.78 : 118.17 = 78.66 : x
2. Step 2: Convert to fraction form
   78.78/118.17 = 78.66/x
3. Step 3: Cross multiply
   78.78x = 118.17 × 78.66
4. Step 4: Simplify right side
   78.78x = 9,295.25
5. Step 5: Solve for x
   x = 9,295.25/78.78
6. Step 6: Final answer
   x = 117.99