Finding the Third Proportional to 865.50 and 1,287

Step by Step Solution

1. Step 1: Write the proportion equation
   865.50 : 1,287 = 1,287 : x
2. Step 2: Convert to fraction form
   865.50/1,287 = 1,287/x
3. Step 3: Cross multiply
   865.50x = 1,287 × 1,287
4. Step 4: Simplify right side
   865.50x = 1,656,369
5. Step 5: Solve for x
   x = 1,656,369/865.50
6. Step 6: Final answer
   x = 1,913.77