Finding the Fourth Proportional to 42.76, 64.16 and 13.88

Step by Step Solution

1. Step 1: Write the proportion equation
   42.76 : 64.16 = 13.88 : x
2. Step 2: Convert to fraction form
   42.76/64.16 = 13.88/x
3. Step 3: Cross multiply
   42.76x = 64.16 × 13.88
4. Step 4: Simplify right side
   42.76x = 890.15
5. Step 5: Solve for x
   x = 890.15/42.76
6. Step 6: Final answer
   x = 20.82