Finding the Fourth Proportional to 1,428.37, 2,139.78 and 810.20

Step by Step Solution

1. Step 1: Write the proportion equation
   1,428.37 : 2,139.78 = 810.20 : x
2. Step 2: Convert to fraction form
   1,428.37/2,139.78 = 810.20/x
3. Step 3: Cross multiply
   1,428.37x = 2,139.78 × 810.20
4. Step 4: Simplify right side
   1,428.37x = 1,733,649.76
5. Step 5: Solve for x
   x = 1,733,649.76/1,428.37
6. Step 6: Final answer
   x = 1,213.73