Finding the Third Proportional to 21,690 and 42,840

Step by Step Solution

1. Step 1: Write the proportion equation
   21,690 : 42,840 = 42,840 : x
2. Step 2: Convert to fraction form
   21,690/42,840 = 42,840/x
3. Step 3: Cross multiply
   21,690x = 42,840 × 42,840
4. Step 4: Simplify right side
   21,690x = 1,835,265,600
5. Step 5: Solve for x
   x = 1,835,265,600/21,690
6. Step 6: Final answer
   x = 84,613.44