Finding the Fourth Proportional to 1,378.80, 1,902.69 and 840.69

Step by Step Solution

1. Step 1: Write the proportion equation
   1,378.80 : 1,902.69 = 840.69 : x
2. Step 2: Convert to fraction form
   1,378.80/1,902.69 = 840.69/x
3. Step 3: Cross multiply
   1,378.80x = 1,902.69 × 840.69
4. Step 4: Simplify right side
   1,378.80x = 1,599,572.46
5. Step 5: Solve for x
   x = 1,599,572.46/1,378.80
6. Step 6: Final answer
   x = 1,160.12