Finding the Third Proportional to 645.50 and 990.50

Step by Step Solution

1. Step 1: Write the proportion equation
   645.50 : 990.50 = 990.50 : x
2. Step 2: Convert to fraction form
   645.50/990.50 = 990.50/x
3. Step 3: Cross multiply
   645.50x = 990.50 × 990.50
4. Step 4: Simplify right side
   645.50x = 981,090.25
5. Step 5: Solve for x
   x = 981,090.25/645.50
6. Step 6: Final answer
   x = 1,519.89