Finding the Fourth Proportional to 1,298.50, 1,947.84 and 640.72

Step by Step Solution

1. Step 1: Write the proportion equation
   1,298.50 : 1,947.84 = 640.72 : x
2. Step 2: Convert to fraction form
   1,298.50/1,947.84 = 640.72/x
3. Step 3: Cross multiply
   1,298.50x = 1,947.84 × 640.72
4. Step 4: Simplify right side
   1,298.50x = 1,248,020.04
5. Step 5: Solve for x
   x = 1,248,020.04/1,298.50
6. Step 6: Final answer
   x = 961.12