Finding the Fourth Proportional to 78.09, 107.69 and 65.83

Step by Step Solution

1. Step 1: Write the proportion equation
   78.09 : 107.69 = 65.83 : x
2. Step 2: Convert to fraction form
   78.09/107.69 = 65.83/x
3. Step 3: Cross multiply
   78.09x = 107.69 × 65.83
4. Step 4: Simplify right side
   78.09x = 7,089.23
5. Step 5: Solve for x
   x = 7,089.23/78.09
6. Step 6: Final answer
   x = 90.78