Finding the Third Proportional to 628.50 and 990.56

Step by Step Solution

1. Step 1: Write the proportion equation
   628.50 : 990.56 = 990.56 : x
2. Step 2: Convert to fraction form
   628.50/990.56 = 990.56/x
3. Step 3: Cross multiply
   628.50x = 990.56 × 990.56
4. Step 4: Simplify right side
   628.50x = 981,214.07
5. Step 5: Solve for x
   x = 981,214.07/628.50
6. Step 6: Final answer
   x = 1,561.20