Finding the Fourth Proportional to 1,139.34, 1,707.80 and 813.72

Step by Step Solution

1. Step 1: Write the proportion equation
   1,139.34 : 1,707.80 = 813.72 : x
2. Step 2: Convert to fraction form
   1,139.34/1,707.80 = 813.72/x
3. Step 3: Cross multiply
   1,139.34x = 1,707.80 × 813.72
4. Step 4: Simplify right side
   1,139.34x = 1,389,671.02
5. Step 5: Solve for x
   x = 1,389,671.02/1,139.34
6. Step 6: Final answer
   x = 1,219.72