Finding the Fourth Proportional to 1,387.80, 1,902.15 and 1,378.20

Step by Step Solution

1. Step 1: Write the proportion equation
   1,387.80 : 1,902.15 = 1,378.20 : x
2. Step 2: Convert to fraction form
   1,387.80/1,902.15 = 1,378.20/x
3. Step 3: Cross multiply
   1,387.80x = 1,902.15 × 1,378.20
4. Step 4: Simplify right side
   1,387.80x = 2,621,543.13
5. Step 5: Solve for x
   x = 2,621,543.13/1,387.80
6. Step 6: Final answer
   x = 1,888.99