Finding the Fourth Proportional to 1,398.24, 1,921.68 and 1,087.20

Step by Step Solution

1. Step 1: Write the proportion equation
   1,398.24 : 1,921.68 = 1,087.20 : x
2. Step 2: Convert to fraction form
   1,398.24/1,921.68 = 1,087.20/x
3. Step 3: Cross multiply
   1,398.24x = 1,921.68 × 1,087.20
4. Step 4: Simplify right side
   1,398.24x = 2,089,250.50
5. Step 5: Solve for x
   x = 2,089,250.50/1,398.24
6. Step 6: Final answer
   x = 1,494.20