Finding the Fourth Proportional to 1,388.26, 1,915.35 and 989.99

Step by Step Solution

1. Step 1: Write the proportion equation
   1,388.26 : 1,915.35 = 989.99 : x
2. Step 2: Convert to fraction form
   1,388.26/1,915.35 = 989.99/x
3. Step 3: Cross multiply
   1,388.26x = 1,915.35 × 989.99
4. Step 4: Simplify right side
   1,388.26x = 1,896,171.24
5. Step 5: Solve for x
   x = 1,896,171.24/1,388.26
6. Step 6: Final answer
   x = 1,365.86