Finding the Third Proportional to 66,991.50 and 139,495.78

Step by Step Solution

1. Step 1: Write the proportion equation
   66,991.50 : 139,495.78 = 139,495.78 : x
2. Step 2: Convert to fraction form
   66,991.50/139,495.78 = 139,495.78/x
3. Step 3: Cross multiply
   66,991.50x = 139,495.78 × 139,495.78
4. Step 4: Simplify right side
   66,991.50x = 19,459,072,986.55
5. Step 5: Solve for x
   x = 19,459,072,986.55/66,991.50
6. Step 6: Final answer
   x = 290,470.78