Finding the Fourth Proportional to 1,378.72, 1,902.56 and 789.20

Step by Step Solution

1. Step 1: Write the proportion equation
   1,378.72 : 1,902.56 = 789.20 : x
2. Step 2: Convert to fraction form
   1,378.72/1,902.56 = 789.20/x
3. Step 3: Cross multiply
   1,378.72x = 1,902.56 × 789.20
4. Step 4: Simplify right side
   1,378.72x = 1,501,500.35
5. Step 5: Solve for x
   x = 1,501,500.35/1,378.72
6. Step 6: Final answer
   x = 1,089.05