Finding the Fourth Proportional to 1,217.50, 1,680.15 and 665.50

Step by Step Solution

1. Step 1: Write the proportion equation
   1,217.50 : 1,680.15 = 665.50 : x
2. Step 2: Convert to fraction form
   1,217.50/1,680.15 = 665.50/x
3. Step 3: Cross multiply
   1,217.50x = 1,680.15 × 665.50
4. Step 4: Simplify right side
   1,217.50x = 1,118,139.83
5. Step 5: Solve for x
   x = 1,118,139.83/1,217.50
6. Step 6: Final answer
   x = 918.39