Finding the Fourth Proportional to 89.91, 123.98 and 81.20

Step by Step Solution

1. Step 1: Write the proportion equation
   89.91 : 123.98 = 81.20 : x
2. Step 2: Convert to fraction form
   89.91/123.98 = 81.20/x
3. Step 3: Cross multiply
   89.91x = 123.98 × 81.20
4. Step 4: Simplify right side
   89.91x = 10,066.15
5. Step 5: Solve for x
   x = 10,066.15/89.91
6. Step 6: Final answer
   x = 111.96