Finding the Fourth Proportional to 1,005.12, 1,506.72 and 426.72

Step by Step Solution

1. Step 1: Write the proportion equation
   1,005.12 : 1,506.72 = 426.72 : x
2. Step 2: Convert to fraction form
   1,005.12/1,506.72 = 426.72/x
3. Step 3: Cross multiply
   1,005.12x = 1,506.72 × 426.72
4. Step 4: Simplify right side
   1,005.12x = 642,947.56
5. Step 5: Solve for x
   x = 642,947.56/1,005.12
6. Step 6: Final answer
   x = 639.67