Finding the Fourth Proportional to 1,086.80, 1,499.56 and 621.20

Step by Step Solution

1. Step 1: Write the proportion equation
   1,086.80 : 1,499.56 = 621.20 : x
2. Step 2: Convert to fraction form
   1,086.80/1,499.56 = 621.20/x
3. Step 3: Cross multiply
   1,086.80x = 1,499.56 × 621.20
4. Step 4: Simplify right side
   1,086.80x = 931,526.67
5. Step 5: Solve for x
   x = 931,526.67/1,086.80
6. Step 6: Final answer
   x = 857.13