Finding the Fourth Proportional to 1,086.17, 1,498.70 and 643.91

Step by Step Solution

1. Step 1: Write the proportion equation
   1,086.17 : 1,498.70 = 643.91 : x
2. Step 2: Convert to fraction form
   1,086.17/1,498.70 = 643.91/x
3. Step 3: Cross multiply
   1,086.17x = 1,498.70 × 643.91
4. Step 4: Simplify right side
   1,086.17x = 965,022.03
5. Step 5: Solve for x
   x = 965,022.03/1,086.17
6. Step 6: Final answer
   x = 888.47