Finding the Fourth Proportional to 1,085.91, 1,498.50 and 643.80

Step by Step Solution

1. Step 1: Write the proportion equation
   1,085.91 : 1,498.50 = 643.80 : x
2. Step 2: Convert to fraction form
   1,085.91/1,498.50 = 643.80/x
3. Step 3: Cross multiply
   1,085.91x = 1,498.50 × 643.80
4. Step 4: Simplify right side
   1,085.91x = 964,734.30
5. Step 5: Solve for x
   x = 964,734.30/1,085.91
6. Step 6: Final answer
   x = 888.41