Finding the Fourth Proportional to 1,105.76, 1,525.56 and 639.76

Step by Step Solution

1. Step 1: Write the proportion equation
   1,105.76 : 1,525.56 = 639.76 : x
2. Step 2: Convert to fraction form
   1,105.76/1,525.56 = 639.76/x
3. Step 3: Cross multiply
   1,105.76x = 1,525.56 × 639.76
4. Step 4: Simplify right side
   1,105.76x = 975,992.27
5. Step 5: Solve for x
   x = 975,992.27/1,105.76
6. Step 6: Final answer
   x = 882.64