Finding the Fourth Proportional to 2,087.80, 3,128.10 and 989.80

Step by Step Solution

1. Step 1: Write the proportion equation
   2,087.80 : 3,128.10 = 989.80 : x
2. Step 2: Convert to fraction form
   2,087.80/3,128.10 = 989.80/x
3. Step 3: Cross multiply
   2,087.80x = 3,128.10 × 989.80
4. Step 4: Simplify right side
   2,087.80x = 3,096,193.38
5. Step 5: Solve for x
   x = 3,096,193.38/2,087.80
6. Step 6: Final answer
   x = 1,482.99