Finding the Fourth Proportional to 1,392.21, 2,078.15 and 1,290.69

Step by Step Solution

1. Step 1: Write the proportion equation
   1,392.21 : 2,078.15 = 1,290.69 : x
2. Step 2: Convert to fraction form
   1,392.21/2,078.15 = 1,290.69/x
3. Step 3: Cross multiply
   1,392.21x = 2,078.15 × 1,290.69
4. Step 4: Simplify right side
   1,392.21x = 2,682,250.65
5. Step 5: Solve for x
   x = 2,682,250.65/1,392.21
6. Step 6: Final answer
   x = 1,926.61