Finding the Fourth Proportional to 1,221.25, 1,685.31 and 661.72

Step by Step Solution

1. Step 1: Write the proportion equation
   1,221.25 : 1,685.31 = 661.72 : x
2. Step 2: Convert to fraction form
   1,221.25/1,685.31 = 661.72/x
3. Step 3: Cross multiply
   1,221.25x = 1,685.31 × 661.72
4. Step 4: Simplify right side
   1,221.25x = 1,115,203.33
5. Step 5: Solve for x
   x = 1,115,203.33/1,221.25
6. Step 6: Final answer
   x = 913.17