Finding the Fourth Proportional to 1,221.57, 1,685.42 and 779.91

Step by Step Solution

1. Step 1: Write the proportion equation
   1,221.57 : 1,685.42 = 779.91 : x
2. Step 2: Convert to fraction form
   1,221.57/1,685.42 = 779.91/x
3. Step 3: Cross multiply
   1,221.57x = 1,685.42 × 779.91
4. Step 4: Simplify right side
   1,221.57x = 1,314,472.01
5. Step 5: Solve for x
   x = 1,314,472.01/1,221.57
6. Step 6: Final answer
   x = 1,076.05