Finding the Fourth Proportional to 1,290.56, 1,934.72 and 640.96

Step by Step Solution

1. Step 1: Write the proportion equation
   1,290.56 : 1,934.72 = 640.96 : x
2. Step 2: Convert to fraction form
   1,290.56/1,934.72 = 640.96/x
3. Step 3: Cross multiply
   1,290.56x = 1,934.72 × 640.96
4. Step 4: Simplify right side
   1,290.56x = 1,240,078.13
5. Step 5: Solve for x
   x = 1,240,078.13/1,290.56
6. Step 6: Final answer
   x = 960.88