Finding the Fourth Proportional to 100.64, 138.78 and 72.61

Step by Step Solution

1. Step 1: Write the proportion equation
   100.64 : 138.78 = 72.61 : x
2. Step 2: Convert to fraction form
   100.64/138.78 = 72.61/x
3. Step 3: Cross multiply
   100.64x = 138.78 × 72.61
4. Step 4: Simplify right side
   100.64x = 10,076.47
5. Step 5: Solve for x
   x = 10,076.47/100.64
6. Step 6: Final answer
   x = 100.12