Finding the Fourth Proportional to 1,105.12, 1,525.28 and 639.40

Step by Step Solution

1. Step 1: Write the proportion equation
   1,105.12 : 1,525.28 = 639.40 : x
2. Step 2: Convert to fraction form
   1,105.12/1,525.28 = 639.40/x
3. Step 3: Cross multiply
   1,105.12x = 1,525.28 × 639.40
4. Step 4: Simplify right side
   1,105.12x = 975,264.03
5. Step 5: Solve for x
   x = 975,264.03/1,105.12
6. Step 6: Final answer
   x = 882.50