Finding the Fourth Proportional to 100.86, 139.90 and 100.05

Step by Step Solution

1. Step 1: Write the proportion equation
   100.86 : 139.90 = 100.05 : x
2. Step 2: Convert to fraction form
   100.86/139.90 = 100.05/x
3. Step 3: Cross multiply
   100.86x = 139.90 × 100.05
4. Step 4: Simplify right side
   100.86x = 13,997.00
5. Step 5: Solve for x
   x = 13,997.00/100.86
6. Step 6: Final answer
   x = 138.78