Finding the Fourth Proportional to 1,323.98, 1,986.45 and 639.50

Step by Step Solution

1. Step 1: Write the proportion equation
   1,323.98 : 1,986.45 = 639.50 : x
2. Step 2: Convert to fraction form
   1,323.98/1,986.45 = 639.50/x
3. Step 3: Cross multiply
   1,323.98x = 1,986.45 × 639.50
4. Step 4: Simplify right side
   1,323.98x = 1,270,334.78
5. Step 5: Solve for x
   x = 1,270,334.78/1,323.98
6. Step 6: Final answer
   x = 959.48