Finding the Fourth Proportional to 28.42, 42.56 and 21.18

Step by Step Solution

1. Step 1: Write the proportion equation
   28.42 : 42.56 = 21.18 : x
2. Step 2: Convert to fraction form
   28.42/42.56 = 21.18/x
3. Step 3: Cross multiply
   28.42x = 42.56 × 21.18
4. Step 4: Simplify right side
   28.42x = 901.42
5. Step 5: Solve for x
   x = 901.42/28.42
6. Step 6: Final answer
   x = 31.72