Finding the Fourth Proportional to 78.69, 117.90 and 42.60

Step by Step Solution

1. Step 1: Write the proportion equation
   78.69 : 117.90 = 42.60 : x
2. Step 2: Convert to fraction form
   78.69/117.90 = 42.60/x
3. Step 3: Cross multiply
   78.69x = 117.90 × 42.60
4. Step 4: Simplify right side
   78.69x = 5,022.54
5. Step 5: Solve for x
   x = 5,022.54/78.69
6. Step 6: Final answer
   x = 63.83