Finding the Fourth Proportional to 1,287.98, 1,932.59 and 638.57

Step by Step Solution

1. Step 1: Write the proportion equation
   1,287.98 : 1,932.59 = 638.57 : x
2. Step 2: Convert to fraction form
   1,287.98/1,932.59 = 638.57/x
3. Step 3: Cross multiply
   1,287.98x = 1,932.59 × 638.57
4. Step 4: Simplify right side
   1,287.98x = 1,234,094.00
5. Step 5: Solve for x
   x = 1,234,094.00/1,287.98
6. Step 6: Final answer
   x = 958.16