Finding the Fourth Proportional to 1,213.86, 1,820.69 and 520.61

Step by Step Solution

1. Step 1: Write the proportion equation
   1,213.86 : 1,820.69 = 520.61 : x
2. Step 2: Convert to fraction form
   1,213.86/1,820.69 = 520.61/x
3. Step 3: Cross multiply
   1,213.86x = 1,820.69 × 520.61
4. Step 4: Simplify right side
   1,213.86x = 947,857.71
5. Step 5: Solve for x
   x = 947,857.71/1,213.86
6. Step 6: Final answer
   x = 780.86