Finding the Fourth Proportional to 1,390.61, 1,918.71 and 830.85

Step by Step Solution

1. Step 1: Write the proportion equation
   1,390.61 : 1,918.71 = 830.85 : x
2. Step 2: Convert to fraction form
   1,390.61/1,918.71 = 830.85/x
3. Step 3: Cross multiply
   1,390.61x = 1,918.71 × 830.85
4. Step 4: Simplify right side
   1,390.61x = 1,594,160.20
5. Step 5: Solve for x
   x = 1,594,160.20/1,390.61
6. Step 6: Final answer
   x = 1,146.38