Finding the Fourth Proportional to 1,689.12, 2,331.18 and 990.72

Step by Step Solution

1. Step 1: Write the proportion equation
   1,689.12 : 2,331.18 = 990.72 : x
2. Step 2: Convert to fraction form
   1,689.12/2,331.18 = 990.72/x
3. Step 3: Cross multiply
   1,689.12x = 2,331.18 × 990.72
4. Step 4: Simplify right side
   1,689.12x = 2,309,546.65
5. Step 5: Solve for x
   x = 2,309,546.65/1,689.12
6. Step 6: Final answer
   x = 1,367.31