Finding the Fourth Proportional to 1,428.72, 1,971.64 and 839.26

Step by Step Solution

1. Step 1: Write the proportion equation
   1,428.72 : 1,971.64 = 839.26 : x
2. Step 2: Convert to fraction form
   1,428.72/1,971.64 = 839.26/x
3. Step 3: Cross multiply
   1,428.72x = 1,971.64 × 839.26
4. Step 4: Simplify right side
   1,428.72x = 1,654,718.59
5. Step 5: Solve for x
   x = 1,654,718.59/1,428.72
6. Step 6: Final answer
   x = 1,158.18