Finding the Fourth Proportional to 86.34, 128.79 and 82.16

Step by Step Solution

1. Step 1: Write the proportion equation
   86.34 : 128.79 = 82.16 : x
2. Step 2: Convert to fraction form
   86.34/128.79 = 82.16/x
3. Step 3: Cross multiply
   86.34x = 128.79 × 82.16
4. Step 4: Simplify right side
   86.34x = 10,581.95
5. Step 5: Solve for x
   x = 10,581.95/86.34
6. Step 6: Final answer
   x = 122.56