Finding the Fourth Proportional to 76.78, 105.89 and 49.15

Step by Step Solution

1. Step 1: Write the proportion equation
   76.78 : 105.89 = 49.15 : x
2. Step 2: Convert to fraction form
   76.78/105.89 = 49.15/x
3. Step 3: Cross multiply
   76.78x = 105.89 × 49.15
4. Step 4: Simplify right side
   76.78x = 5,204.49
5. Step 5: Solve for x
   x = 5,204.49/76.78
6. Step 6: Final answer
   x = 67.79