Finding the Fourth Proportional to 1,290.82, 1,935.54 and 640.76

Step by Step Solution

1. Step 1: Write the proportion equation
   1,290.82 : 1,935.54 = 640.76 : x
2. Step 2: Convert to fraction form
   1,290.82/1,935.54 = 640.76/x
3. Step 3: Cross multiply
   1,290.82x = 1,935.54 × 640.76
4. Step 4: Simplify right side
   1,290.82x = 1,240,216.61
5. Step 5: Solve for x
   x = 1,240,216.61/1,290.82
6. Step 6: Final answer
   x = 960.80