Finding the Fourth Proportional to 1,387.96, 1,915.32 and 828.80

Step by Step Solution

1. Step 1: Write the proportion equation
   1,387.96 : 1,915.32 = 828.80 : x
2. Step 2: Convert to fraction form
   1,387.96/1,915.32 = 828.80/x
3. Step 3: Cross multiply
   1,387.96x = 1,915.32 × 828.80
4. Step 4: Simplify right side
   1,387.96x = 1,587,417.22
5. Step 5: Solve for x
   x = 1,587,417.22/1,387.96
6. Step 6: Final answer
   x = 1,143.71