Finding the Fourth Proportional to 85.30, 128.15 and 82.87

Step by Step Solution

1. Step 1: Write the proportion equation
   85.30 : 128.15 = 82.87 : x
2. Step 2: Convert to fraction form
   85.30/128.15 = 82.87/x
3. Step 3: Cross multiply
   85.30x = 128.15 × 82.87
4. Step 4: Simplify right side
   85.30x = 10,619.79
5. Step 5: Solve for x
   x = 10,619.79/85.30
6. Step 6: Final answer
   x = 124.50