Finding the Fourth Proportional to 1,012.89, 1,397.14 and 639.55

Step by Step Solution

1. Step 1: Write the proportion equation
   1,012.89 : 1,397.14 = 639.55 : x
2. Step 2: Convert to fraction form
   1,012.89/1,397.14 = 639.55/x
3. Step 3: Cross multiply
   1,012.89x = 1,397.14 × 639.55
4. Step 4: Simplify right side
   1,012.89x = 893,540.89
5. Step 5: Solve for x
   x = 893,540.89/1,012.89
6. Step 6: Final answer
   x = 882.17