Finding the Fourth Proportional to 1,388.24, 1,915.80 and 790.80

Step by Step Solution

1. Step 1: Write the proportion equation
   1,388.24 : 1,915.80 = 790.80 : x
2. Step 2: Convert to fraction form
   1,388.24/1,915.80 = 790.80/x
3. Step 3: Cross multiply
   1,388.24x = 1,915.80 × 790.80
4. Step 4: Simplify right side
   1,388.24x = 1,515,021.82
5. Step 5: Solve for x
   x = 1,515,021.82/1,388.24
6. Step 6: Final answer
   x = 1,091.32