Finding the Fourth Proportional to 128.82, 192.86 and 99.78

Step by Step Solution

1. Step 1: Write the proportion equation
   128.82 : 192.86 = 99.78 : x
2. Step 2: Convert to fraction form
   128.82/192.86 = 99.78/x
3. Step 3: Cross multiply
   128.82x = 192.86 × 99.78
4. Step 4: Simplify right side
   128.82x = 19,243.57
5. Step 5: Solve for x
   x = 19,243.57/128.82
6. Step 6: Final answer
   x = 149.38