Finding the Fourth Proportional to 1,428.83, 1,971.57 and 839.55

Step by Step Solution

1. Step 1: Write the proportion equation
   1,428.83 : 1,971.57 = 839.55 : x
2. Step 2: Convert to fraction form
   1,428.83/1,971.57 = 839.55/x
3. Step 3: Cross multiply
   1,428.83x = 1,971.57 × 839.55
4. Step 4: Simplify right side
   1,428.83x = 1,655,231.59
5. Step 5: Solve for x
   x = 1,655,231.59/1,428.83
6. Step 6: Final answer
   x = 1,158.45