Finding the Fourth Proportional to 1,378.77, 1,902.70 and 789.30

Step by Step Solution

1. Step 1: Write the proportion equation
   1,378.77 : 1,902.70 = 789.30 : x
2. Step 2: Convert to fraction form
   1,378.77/1,902.70 = 789.30/x
3. Step 3: Cross multiply
   1,378.77x = 1,902.70 × 789.30
4. Step 4: Simplify right side
   1,378.77x = 1,501,797.16
5. Step 5: Solve for x
   x = 1,501,797.16/1,378.77
6. Step 6: Final answer
   x = 1,089.23