Finding the Fourth Proportional to 1,109.78, 1,531.43 and 644.02

Step by Step Solution

1. Step 1: Write the proportion equation
   1,109.78 : 1,531.43 = 644.02 : x
2. Step 2: Convert to fraction form
   1,109.78/1,531.43 = 644.02/x
3. Step 3: Cross multiply
   1,109.78x = 1,531.43 × 644.02
4. Step 4: Simplify right side
   1,109.78x = 986,271.55
5. Step 5: Solve for x
   x = 986,271.55/1,109.78
6. Step 6: Final answer
   x = 888.71