Finding the Fourth Proportional to 128.78, 192.38 and 128.15

Step by Step Solution

1. Step 1: Write the proportion equation
   128.78 : 192.38 = 128.15 : x
2. Step 2: Convert to fraction form
   128.78/192.38 = 128.15/x
3. Step 3: Cross multiply
   128.78x = 192.38 × 128.15
4. Step 4: Simplify right side
   128.78x = 24,651.89
5. Step 5: Solve for x
   x = 24,651.89/128.78
6. Step 6: Final answer
   x = 191.43