Finding the Third Proportional to 211.50 and 421.50

Step by Step Solution

1. Step 1: Write the proportion equation
   211.50 : 421.50 = 421.50 : x
2. Step 2: Convert to fraction form
   211.50/421.50 = 421.50/x
3. Step 3: Cross multiply
   211.50x = 421.50 × 421.50
4. Step 4: Simplify right side
   211.50x = 177,662.25
5. Step 5: Solve for x
   x = 177,662.25/211.50
6. Step 6: Final answer
   x = 840.01