Finding the Fourth Proportional to 139.43, 208.78 and 78.27

Step by Step Solution

1. Step 1: Write the proportion equation
   139.43 : 208.78 = 78.27 : x
2. Step 2: Convert to fraction form
   139.43/208.78 = 78.27/x
3. Step 3: Cross multiply
   139.43x = 208.78 × 78.27
4. Step 4: Simplify right side
   139.43x = 16,341.31
5. Step 5: Solve for x
   x = 16,341.31/139.43
6. Step 6: Final answer
   x = 117.21