Finding the Fourth Proportional to 85.48, 128.78 and 77.67

Step by Step Solution

1. Step 1: Write the proportion equation
   85.48 : 128.78 = 77.67 : x
2. Step 2: Convert to fraction form
   85.48/128.78 = 77.67/x
3. Step 3: Cross multiply
   85.48x = 128.78 × 77.67
4. Step 4: Simplify right side
   85.48x = 10,002.34
5. Step 5: Solve for x
   x = 10,002.34/85.48
6. Step 6: Final answer
   x = 117.01