Finding the Third Proportional to 420.56 and 618.56

Step by Step Solution

1. Step 1: Write the proportion equation
   420.56 : 618.56 = 618.56 : x
2. Step 2: Convert to fraction form
   420.56/618.56 = 618.56/x
3. Step 3: Cross multiply
   420.56x = 618.56 × 618.56
4. Step 4: Simplify right side
   420.56x = 382,619.57
5. Step 5: Solve for x
   x = 382,619.57/420.56
6. Step 6: Final answer
   x = 909.78