Finding the Fourth Proportional to 78.56, 117.83 and 20.78

Step by Step Solution

1. Step 1: Write the proportion equation
   78.56 : 117.83 = 20.78 : x
2. Step 2: Convert to fraction form
   78.56/117.83 = 20.78/x
3. Step 3: Cross multiply
   78.56x = 117.83 × 20.78
4. Step 4: Simplify right side
   78.56x = 2,448.96
5. Step 5: Solve for x
   x = 2,448.96/78.56
6. Step 6: Final answer
   x = 31.17