Finding the Fourth Proportional to 1,012.69, 1,397.52 and 639.28

Step by Step Solution

1. Step 1: Write the proportion equation
   1,012.69 : 1,397.52 = 639.28 : x
2. Step 2: Convert to fraction form
   1,012.69/1,397.52 = 639.28/x
3. Step 3: Cross multiply
   1,012.69x = 1,397.52 × 639.28
4. Step 4: Simplify right side
   1,012.69x = 893,406.59
5. Step 5: Solve for x
   x = 893,406.59/1,012.69
6. Step 6: Final answer
   x = 882.21