Finding the Fourth Proportional to 1,388.68, 1,915.48 and 828.71

Step by Step Solution

1. Step 1: Write the proportion equation
   1,388.68 : 1,915.48 = 828.71 : x
2. Step 2: Convert to fraction form
   1,388.68/1,915.48 = 828.71/x
3. Step 3: Cross multiply
   1,388.68x = 1,915.48 × 828.71
4. Step 4: Simplify right side
   1,388.68x = 1,587,380.15
5. Step 5: Solve for x
   x = 1,587,380.15/1,388.68
6. Step 6: Final answer
   x = 1,143.09