Finding the Fourth Proportional to 1,308.18, 1,959.78 and 780

Step by Step Solution

1. Step 1: Write the proportion equation
   1,308.18 : 1,959.78 = 780 : x
2. Step 2: Convert to fraction form
   1,308.18/1,959.78 = 780/x
3. Step 3: Cross multiply
   1,308.18x = 1,959.78 × 780
4. Step 4: Simplify right side
   1,308.18x = 1,528,628.40
5. Step 5: Solve for x
   x = 1,528,628.40/1,308.18
6. Step 6: Final answer
   x = 1,168.52