Finding the Fourth Proportional to 1,428.78, 1,971.77 and 839.31

Step by Step Solution

1. Step 1: Write the proportion equation
   1,428.78 : 1,971.77 = 839.31 : x
2. Step 2: Convert to fraction form
   1,428.78/1,971.77 = 839.31/x
3. Step 3: Cross multiply
   1,428.78x = 1,971.77 × 839.31
4. Step 4: Simplify right side
   1,428.78x = 1,654,928.38
5. Step 5: Solve for x
   x = 1,654,928.38/1,428.78
6. Step 6: Final answer
   x = 1,158.28