Finding the Fourth Proportional to 1,002.78, 1,506.60 and 638.28

Step by Step Solution

1. Step 1: Write the proportion equation
   1,002.78 : 1,506.60 = 638.28 : x
2. Step 2: Convert to fraction form
   1,002.78/1,506.60 = 638.28/x
3. Step 3: Cross multiply
   1,002.78x = 1,506.60 × 638.28
4. Step 4: Simplify right side
   1,002.78x = 961,632.65
5. Step 5: Solve for x
   x = 961,632.65/1,002.78
6. Step 6: Final answer
   x = 958.97