Finding the Fourth Proportional to 85.70, 128.82 and 83.81

Step by Step Solution

1. Step 1: Write the proportion equation
   85.70 : 128.82 = 83.81 : x
2. Step 2: Convert to fraction form
   85.70/128.82 = 83.81/x
3. Step 3: Cross multiply
   85.70x = 128.82 × 83.81
4. Step 4: Simplify right side
   85.70x = 10,796.40
5. Step 5: Solve for x
   x = 10,796.40/85.70
6. Step 6: Final answer
   x = 125.98