Finding the Fourth Proportional to 1,012.28, 1,396.82 and 639.12

Step by Step Solution

1. Step 1: Write the proportion equation
   1,012.28 : 1,396.82 = 639.12 : x
2. Step 2: Convert to fraction form
   1,012.28/1,396.82 = 639.12/x
3. Step 3: Cross multiply
   1,012.28x = 1,396.82 × 639.12
4. Step 4: Simplify right side
   1,012.28x = 892,735.60
5. Step 5: Solve for x
   x = 892,735.60/1,012.28
6. Step 6: Final answer
   x = 881.91