Finding the Fourth Proportional to 2,139.72, 3,209.56 and 1,620.76

Step by Step Solution

1. Step 1: Write the proportion equation
   2,139.72 : 3,209.56 = 1,620.76 : x
2. Step 2: Convert to fraction form
   2,139.72/3,209.56 = 1,620.76/x
3. Step 3: Cross multiply
   2,139.72x = 3,209.56 × 1,620.76
4. Step 4: Simplify right side
   2,139.72x = 5,201,926.47
5. Step 5: Solve for x
   x = 5,201,926.47/2,139.72
6. Step 6: Final answer
   x = 2,431.12