Finding the Fourth Proportional to 1,131.18, 1,695.15 and 643.20

Step by Step Solution

1. Step 1: Write the proportion equation
   1,131.18 : 1,695.15 = 643.20 : x
2. Step 2: Convert to fraction form
   1,131.18/1,695.15 = 643.20/x
3. Step 3: Cross multiply
   1,131.18x = 1,695.15 × 643.20
4. Step 4: Simplify right side
   1,131.18x = 1,090,320.48
5. Step 5: Solve for x
   x = 1,090,320.48/1,131.18
6. Step 6: Final answer
   x = 963.88