Finding the Fourth Proportional to 100.24, 138.24 and 78.42

Step by Step Solution

1. Step 1: Write the proportion equation
   100.24 : 138.24 = 78.42 : x
2. Step 2: Convert to fraction form
   100.24/138.24 = 78.42/x
3. Step 3: Cross multiply
   100.24x = 138.24 × 78.42
4. Step 4: Simplify right side
   100.24x = 10,840.78
5. Step 5: Solve for x
   x = 10,840.78/100.24
6. Step 6: Final answer
   x = 108.15