Finding the Fourth Proportional to 1,005.20, 1,386.05 and 631.72

Step by Step Solution

1. Step 1: Write the proportion equation
   1,005.20 : 1,386.05 = 631.72 : x
2. Step 2: Convert to fraction form
   1,005.20/1,386.05 = 631.72/x
3. Step 3: Cross multiply
   1,005.20x = 1,386.05 × 631.72
4. Step 4: Simplify right side
   1,005.20x = 875,588.88
5. Step 5: Solve for x
   x = 875,588.88/1,005.20
6. Step 6: Final answer
   x = 871.06