Finding the Fourth Proportional to 1,428.88, 1,970.96 and 839.28

Step by Step Solution

1. Step 1: Write the proportion equation
   1,428.88 : 1,970.96 = 839.28 : x
2. Step 2: Convert to fraction form
   1,428.88/1,970.96 = 839.28/x
3. Step 3: Cross multiply
   1,428.88x = 1,970.96 × 839.28
4. Step 4: Simplify right side
   1,428.88x = 1,654,187.31
5. Step 5: Solve for x
   x = 1,654,187.31/1,428.88
6. Step 6: Final answer
   x = 1,157.68