Finding the Fourth Proportional to 1,290.78, 1,934.49 and 520.86

Step by Step Solution

1. Step 1: Write the proportion equation
   1,290.78 : 1,934.49 = 520.86 : x
2. Step 2: Convert to fraction form
   1,290.78/1,934.49 = 520.86/x
3. Step 3: Cross multiply
   1,290.78x = 1,934.49 × 520.86
4. Step 4: Simplify right side
   1,290.78x = 1,007,598.46
5. Step 5: Solve for x
   x = 1,007,598.46/1,290.78
6. Step 6: Final answer
   x = 780.61