Finding the Third Proportional to 639.50 and 991.50

Step by Step Solution

1. Step 1: Write the proportion equation
   639.50 : 991.50 = 991.50 : x
2. Step 2: Convert to fraction form
   639.50/991.50 = 991.50/x
3. Step 3: Cross multiply
   639.50x = 991.50 × 991.50
4. Step 4: Simplify right side
   639.50x = 983,072.25
5. Step 5: Solve for x
   x = 983,072.25/639.50
6. Step 6: Final answer
   x = 1,537.25