Finding the Fourth Proportional to 1,298.78, 1,792.31 and 709.31

Step by Step Solution

1. Step 1: Write the proportion equation
   1,298.78 : 1,792.31 = 709.31 : x
2. Step 2: Convert to fraction form
   1,298.78/1,792.31 = 709.31/x
3. Step 3: Cross multiply
   1,298.78x = 1,792.31 × 709.31
4. Step 4: Simplify right side
   1,298.78x = 1,271,290.90
5. Step 5: Solve for x
   x = 1,271,290.90/1,298.78
6. Step 6: Final answer
   x = 978.84