Finding the Fourth Proportional to 1,378.66, 1,902.55 and 789.20

Step by Step Solution

1. Step 1: Write the proportion equation
   1,378.66 : 1,902.55 = 789.20 : x
2. Step 2: Convert to fraction form
   1,378.66/1,902.55 = 789.20/x
3. Step 3: Cross multiply
   1,378.66x = 1,902.55 × 789.20
4. Step 4: Simplify right side
   1,378.66x = 1,501,492.46
5. Step 5: Solve for x
   x = 1,501,492.46/1,378.66
6. Step 6: Final answer
   x = 1,089.10