Finding the Fourth Proportional to 1,109.90, 1,531.41 and 643.88

Step by Step Solution

1. Step 1: Write the proportion equation
   1,109.90 : 1,531.41 = 643.88 : x
2. Step 2: Convert to fraction form
   1,109.90/1,531.41 = 643.88/x
3. Step 3: Cross multiply
   1,109.90x = 1,531.41 × 643.88
4. Step 4: Simplify right side
   1,109.90x = 986,036.61
5. Step 5: Solve for x
   x = 986,036.61/1,109.90
6. Step 6: Final answer
   x = 888.41