Finding the Fourth Proportional to 1,399.75, 1,929.61 and 978.80

Step by Step Solution

1. Step 1: Write the proportion equation
   1,399.75 : 1,929.61 = 978.80 : x
2. Step 2: Convert to fraction form
   1,399.75/1,929.61 = 978.80/x
3. Step 3: Cross multiply
   1,399.75x = 1,929.61 × 978.80
4. Step 4: Simplify right side
   1,399.75x = 1,888,693.84
5. Step 5: Solve for x
   x = 1,888,693.84/1,399.75
6. Step 6: Final answer
   x = 1,349.31