Finding the Fourth Proportional to 1,105.20, 1,659.01 and 643.50

Step by Step Solution

1. Step 1: Write the proportion equation
   1,105.20 : 1,659.01 = 643.50 : x
2. Step 2: Convert to fraction form
   1,105.20/1,659.01 = 643.50/x
3. Step 3: Cross multiply
   1,105.20x = 1,659.01 × 643.50
4. Step 4: Simplify right side
   1,105.20x = 1,067,572.94
5. Step 5: Solve for x
   x = 1,067,572.94/1,105.20
6. Step 6: Final answer
   x = 965.95