Finding the Fourth Proportional to 1,223.69, 1,688.78 and 781.97

Step by Step Solution

1. Step 1: Write the proportion equation
   1,223.69 : 1,688.78 = 781.97 : x
2. Step 2: Convert to fraction form
   1,223.69/1,688.78 = 781.97/x
3. Step 3: Cross multiply
   1,223.69x = 1,688.78 × 781.97
4. Step 4: Simplify right side
   1,223.69x = 1,320,568.81
5. Step 5: Solve for x
   x = 1,320,568.81/1,223.69
6. Step 6: Final answer
   x = 1,079.17