Finding the Fourth Proportional to 1,443.40, 1,991.89 and 780.25

Step by Step Solution

1. Step 1: Write the proportion equation
   1,443.40 : 1,991.89 = 780.25 : x
2. Step 2: Convert to fraction form
   1,443.40/1,991.89 = 780.25/x
3. Step 3: Cross multiply
   1,443.40x = 1,991.89 × 780.25
4. Step 4: Simplify right side
   1,443.40x = 1,554,172.17
5. Step 5: Solve for x
   x = 1,554,172.17/1,443.40
6. Step 6: Final answer
   x = 1,076.74