Finding the Fourth Proportional to 1,005.69, 1,509.18 and 428.57

Step by Step Solution

1. Step 1: Write the proportion equation
   1,005.69 : 1,509.18 = 428.57 : x
2. Step 2: Convert to fraction form
   1,005.69/1,509.18 = 428.57/x
3. Step 3: Cross multiply
   1,005.69x = 1,509.18 × 428.57
4. Step 4: Simplify right side
   1,005.69x = 646,789.27
5. Step 5: Solve for x
   x = 646,789.27/1,005.69
6. Step 6: Final answer
   x = 643.13