Finding the Fourth Proportional to 1,388.72, 1,915.94 and 828.80

Step by Step Solution

1. Step 1: Write the proportion equation
   1,388.72 : 1,915.94 = 828.80 : x
2. Step 2: Convert to fraction form
   1,388.72/1,915.94 = 828.80/x
3. Step 3: Cross multiply
   1,388.72x = 1,915.94 × 828.80
4. Step 4: Simplify right side
   1,388.72x = 1,587,931.07
5. Step 5: Solve for x
   x = 1,587,931.07/1,388.72
6. Step 6: Final answer
   x = 1,143.45