Finding the Fourth Proportional to 1,212.78, 1,673.61 and 688.80

Step by Step Solution

1. Step 1: Write the proportion equation
   1,212.78 : 1,673.61 = 688.80 : x
2. Step 2: Convert to fraction form
   1,212.78/1,673.61 = 688.80/x
3. Step 3: Cross multiply
   1,212.78x = 1,673.61 × 688.80
4. Step 4: Simplify right side
   1,212.78x = 1,152,782.57
5. Step 5: Solve for x
   x = 1,152,782.57/1,212.78
6. Step 6: Final answer
   x = 950.53