Finding the Fourth Proportional to 1,287.57, 1,930.40 and 638.15

Step by Step Solution

1. Step 1: Write the proportion equation
   1,287.57 : 1,930.40 = 638.15 : x
2. Step 2: Convert to fraction form
   1,287.57/1,930.40 = 638.15/x
3. Step 3: Cross multiply
   1,287.57x = 1,930.40 × 638.15
4. Step 4: Simplify right side
   1,287.57x = 1,231,884.76
5. Step 5: Solve for x
   x = 1,231,884.76/1,287.57
6. Step 6: Final answer
   x = 956.75