Finding the Fourth Proportional to 1,085.78, 1,498.34 and 643.70

Step by Step Solution

1. Step 1: Write the proportion equation
   1,085.78 : 1,498.34 = 643.70 : x
2. Step 2: Convert to fraction form
   1,085.78/1,498.34 = 643.70/x
3. Step 3: Cross multiply
   1,085.78x = 1,498.34 × 643.70
4. Step 4: Simplify right side
   1,085.78x = 964,481.46
5. Step 5: Solve for x
   x = 964,481.46/1,085.78
6. Step 6: Final answer
   x = 888.28