Finding the Fourth Proportional to 139.32, 208.91 and 78.50

Step by Step Solution

1. Step 1: Write the proportion equation
   139.32 : 208.91 = 78.50 : x
2. Step 2: Convert to fraction form
   139.32/208.91 = 78.50/x
3. Step 3: Cross multiply
   139.32x = 208.91 × 78.50
4. Step 4: Simplify right side
   139.32x = 16,400.15
5. Step 5: Solve for x
   x = 16,400.15/139.32
6. Step 6: Final answer
   x = 117.72