Finding the Fourth Proportional to 1,112.80, 1,668.72 and 839.20

Step by Step Solution

1. Step 1: Write the proportion equation
   1,112.80 : 1,668.72 = 839.20 : x
2. Step 2: Convert to fraction form
   1,112.80/1,668.72 = 839.20/x
3. Step 3: Cross multiply
   1,112.80x = 1,668.72 × 839.20
4. Step 4: Simplify right side
   1,112.80x = 1,400,389.82
5. Step 5: Solve for x
   x = 1,400,389.82/1,112.80
6. Step 6: Final answer
   x = 1,258.44