Finding the Fourth Proportional to 1,390.46, 1,908.61 and 1,229.57

Step by Step Solution

1. Step 1: Write the proportion equation
   1,390.46 : 1,908.61 = 1,229.57 : x
2. Step 2: Convert to fraction form
   1,390.46/1,908.61 = 1,229.57/x
3. Step 3: Cross multiply
   1,390.46x = 1,908.61 × 1,229.57
4. Step 4: Simplify right side
   1,390.46x = 2,346,760.05
5. Step 5: Solve for x
   x = 2,346,760.05/1,390.46
6. Step 6: Final answer
   x = 1,687.76