Finding the Fourth Proportional to 1,320.88, 1,821.72 and 990.12

Step by Step Solution

1. Step 1: Write the proportion equation
   1,320.88 : 1,821.72 = 990.12 : x
2. Step 2: Convert to fraction form
   1,320.88/1,821.72 = 990.12/x
3. Step 3: Cross multiply
   1,320.88x = 1,821.72 × 990.12
4. Step 4: Simplify right side
   1,320.88x = 1,803,721.41
5. Step 5: Solve for x
   x = 1,803,721.41/1,320.88
6. Step 6: Final answer
   x = 1,365.55