Finding the Fourth Proportional to 100.82, 139.19 and 78.80

Step by Step Solution

1. Step 1: Write the proportion equation
   100.82 : 139.19 = 78.80 : x
2. Step 2: Convert to fraction form
   100.82/139.19 = 78.80/x
3. Step 3: Cross multiply
   100.82x = 139.19 × 78.80
4. Step 4: Simplify right side
   100.82x = 10,967.08
5. Step 5: Solve for x
   x = 10,967.08/100.82
6. Step 6: Final answer
   x = 108.78