Finding the Fourth Proportional to 2,086.20, 3,129.34 and 931.72

Step by Step Solution

1. Step 1: Write the proportion equation
   2,086.20 : 3,129.34 = 931.72 : x
2. Step 2: Convert to fraction form
   2,086.20/3,129.34 = 931.72/x
3. Step 3: Cross multiply
   2,086.20x = 3,129.34 × 931.72
4. Step 4: Simplify right side
   2,086.20x = 2,915,668.66
5. Step 5: Solve for x
   x = 2,915,668.66/2,086.20
6. Step 6: Final answer
   x = 1,397.60