Finding the Fourth Proportional to 1,085.78, 1,498.41 and 643.65

Step by Step Solution

1. Step 1: Write the proportion equation
   1,085.78 : 1,498.41 = 643.65 : x
2. Step 2: Convert to fraction form
   1,085.78/1,498.41 = 643.65/x
3. Step 3: Cross multiply
   1,085.78x = 1,498.41 × 643.65
4. Step 4: Simplify right side
   1,085.78x = 964,451.60
5. Step 5: Solve for x
   x = 964,451.60/1,085.78
6. Step 6: Final answer
   x = 888.26