Finding the Third Proportional to 915 and 1,221.50

Step by Step Solution

1. Step 1: Write the proportion equation
   915 : 1,221.50 = 1,221.50 : x
2. Step 2: Convert to fraction form
   915/1,221.50 = 1,221.50/x
3. Step 3: Cross multiply
   915x = 1,221.50 × 1,221.50
4. Step 4: Simplify right side
   915x = 1,492,062.25
5. Step 5: Solve for x
   x = 1,492,062.25/915
6. Step 6: Final answer
   x = 1,630.67