Finding the Third Proportional to 643 and 1,388.50

Step by Step Solution

1. Step 1: Write the proportion equation
   643 : 1,388.50 = 1,388.50 : x
2. Step 2: Convert to fraction form
   643/1,388.50 = 1,388.50/x
3. Step 3: Cross multiply
   643x = 1,388.50 × 1,388.50
4. Step 4: Simplify right side
   643x = 1,927,932.25
5. Step 5: Solve for x
   x = 1,927,932.25/643
6. Step 6: Final answer
   x = 2,998.34