Finding the Fourth Proportional to 1,392.81, 1,920.69 and 921.12

Step by Step Solution

1. Step 1: Write the proportion equation
   1,392.81 : 1,920.69 = 921.12 : x
2. Step 2: Convert to fraction form
   1,392.81/1,920.69 = 921.12/x
3. Step 3: Cross multiply
   1,392.81x = 1,920.69 × 921.12
4. Step 4: Simplify right side
   1,392.81x = 1,769,185.97
5. Step 5: Solve for x
   x = 1,769,185.97/1,392.81
6. Step 6: Final answer
   x = 1,270.23