Finding the Fourth Proportional to 1,105.38, 1,525.60 and 639.90

Step by Step Solution

1. Step 1: Write the proportion equation
   1,105.38 : 1,525.60 = 639.90 : x
2. Step 2: Convert to fraction form
   1,105.38/1,525.60 = 639.90/x
3. Step 3: Cross multiply
   1,105.38x = 1,525.60 × 639.90
4. Step 4: Simplify right side
   1,105.38x = 976,222.21
5. Step 5: Solve for x
   x = 976,222.21/1,105.38
6. Step 6: Final answer
   x = 883.16