Finding the Fourth Proportional to 1,313.72, 1,812.78 and 789.72

Step by Step Solution

1. Step 1: Write the proportion equation
   1,313.72 : 1,812.78 = 789.72 : x
2. Step 2: Convert to fraction form
   1,313.72/1,812.78 = 789.72/x
3. Step 3: Cross multiply
   1,313.72x = 1,812.78 × 789.72
4. Step 4: Simplify right side
   1,313.72x = 1,431,588.62
5. Step 5: Solve for x
   x = 1,431,588.62/1,313.72
6. Step 6: Final answer
   x = 1,089.72