Finding the Fourth Proportional to 1,087.34, 1,500.78 and 639.30

Step by Step Solution

1. Step 1: Write the proportion equation
   1,087.34 : 1,500.78 = 639.30 : x
2. Step 2: Convert to fraction form
   1,087.34/1,500.78 = 639.30/x
3. Step 3: Cross multiply
   1,087.34x = 1,500.78 × 639.30
4. Step 4: Simplify right side
   1,087.34x = 959,456.68
5. Step 5: Solve for x
   x = 959,456.68/1,087.34
6. Step 6: Final answer
   x = 882.39