Finding the Fourth Proportional to 1,139.78, 1,573.89 and 720.88

Step by Step Solution

1. Step 1: Write the proportion equation
   1,139.78 : 1,573.89 = 720.88 : x
2. Step 2: Convert to fraction form
   1,139.78/1,573.89 = 720.88/x
3. Step 3: Cross multiply
   1,139.78x = 1,573.89 × 720.88
4. Step 4: Simplify right side
   1,139.78x = 1,134,585.82
5. Step 5: Solve for x
   x = 1,134,585.82/1,139.78
6. Step 6: Final answer
   x = 995.44