Finding the Fourth Proportional to 1,188.78, 1,781.31 and 928.15

Step by Step Solution

1. Step 1: Write the proportion equation
   1,188.78 : 1,781.31 = 928.15 : x
2. Step 2: Convert to fraction form
   1,188.78/1,781.31 = 928.15/x
3. Step 3: Cross multiply
   1,188.78x = 1,781.31 × 928.15
4. Step 4: Simplify right side
   1,188.78x = 1,653,322.88
5. Step 5: Solve for x
   x = 1,653,322.88/1,188.78
6. Step 6: Final answer
   x = 1,390.77