Finding the Fourth Proportional to 1,387.10, 1,910.31 and 1,200.80

Step by Step Solution

1. Step 1: Write the proportion equation
   1,387.10 : 1,910.31 = 1,200.80 : x
2. Step 2: Convert to fraction form
   1,387.10/1,910.31 = 1,200.80/x
3. Step 3: Cross multiply
   1,387.10x = 1,910.31 × 1,200.80
4. Step 4: Simplify right side
   1,387.10x = 2,293,900.25
5. Step 5: Solve for x
   x = 2,293,900.25/1,387.10
6. Step 6: Final answer
   x = 1,653.74