Finding the Fourth Proportional to 1,085.81, 1,498.64 and 643.98

Step by Step Solution

1. Step 1: Write the proportion equation
   1,085.81 : 1,498.64 = 643.98 : x
2. Step 2: Convert to fraction form
   1,085.81/1,498.64 = 643.98/x
3. Step 3: Cross multiply
   1,085.81x = 1,498.64 × 643.98
4. Step 4: Simplify right side
   1,085.81x = 965,096.59
5. Step 5: Solve for x
   x = 965,096.59/1,085.81
6. Step 6: Final answer
   x = 888.83