Finding the Fourth Proportional to 1,288.71, 1,931.27 and 638.79

Step by Step Solution

1. Step 1: Write the proportion equation
   1,288.71 : 1,931.27 = 638.79 : x
2. Step 2: Convert to fraction form
   1,288.71/1,931.27 = 638.79/x
3. Step 3: Cross multiply
   1,288.71x = 1,931.27 × 638.79
4. Step 4: Simplify right side
   1,288.71x = 1,233,672.77
5. Step 5: Solve for x
   x = 1,233,672.77/1,288.71
6. Step 6: Final answer
   x = 957.29