Finding the Fourth Proportional to 1,011.89, 1,395.77 and 638.55

Step by Step Solution

1. Step 1: Write the proportion equation
   1,011.89 : 1,395.77 = 638.55 : x
2. Step 2: Convert to fraction form
   1,011.89/1,395.77 = 638.55/x
3. Step 3: Cross multiply
   1,011.89x = 1,395.77 × 638.55
4. Step 4: Simplify right side
   1,011.89x = 891,265.74
5. Step 5: Solve for x
   x = 891,265.74/1,011.89
6. Step 6: Final answer
   x = 880.80