Finding the Fourth Proportional to 1,378.90, 1,902.88 and 789.42

Step by Step Solution

1. Step 1: Write the proportion equation
   1,378.90 : 1,902.88 = 789.42 : x
2. Step 2: Convert to fraction form
   1,378.90/1,902.88 = 789.42/x
3. Step 3: Cross multiply
   1,378.90x = 1,902.88 × 789.42
4. Step 4: Simplify right side
   1,378.90x = 1,502,171.53
5. Step 5: Solve for x
   x = 1,502,171.53/1,378.90
6. Step 6: Final answer
   x = 1,089.40