Finding the Fourth Proportional to 139.12, 208.71 and 78.17

Step by Step Solution

1. Step 1: Write the proportion equation
   139.12 : 208.71 = 78.17 : x
2. Step 2: Convert to fraction form
   139.12/208.71 = 78.17/x
3. Step 3: Cross multiply
   139.12x = 208.71 × 78.17
4. Step 4: Simplify right side
   139.12x = 16,313.82
5. Step 5: Solve for x
   x = 16,313.82/139.12
6. Step 6: Final answer
   x = 117.27