Finding the Fourth Proportional to 2,591.50, 3,887.28 and 643.72

Step by Step Solution

1. Step 1: Write the proportion equation
   2,591.50 : 3,887.28 = 643.72 : x
2. Step 2: Convert to fraction form
   2,591.50/3,887.28 = 643.72/x
3. Step 3: Cross multiply
   2,591.50x = 3,887.28 × 643.72
4. Step 4: Simplify right side
   2,591.50x = 2,502,319.88
5. Step 5: Solve for x
   x = 2,502,319.88/2,591.50
6. Step 6: Final answer
   x = 965.59