Finding the Fourth Proportional to 82.78, 123.24 and 81.64

Step by Step Solution

1. Step 1: Write the proportion equation
   82.78 : 123.24 = 81.64 : x
2. Step 2: Convert to fraction form
   82.78/123.24 = 81.64/x
3. Step 3: Cross multiply
   82.78x = 123.24 × 81.64
4. Step 4: Simplify right side
   82.78x = 10,061.31
5. Step 5: Solve for x
   x = 10,061.31/82.78
6. Step 6: Final answer
   x = 121.54