Finding the Fourth Proportional to 2,142.40, 3,210.15 and 1,215.20

Step by Step Solution

1. Step 1: Write the proportion equation
   2,142.40 : 3,210.15 = 1,215.20 : x
2. Step 2: Convert to fraction form
   2,142.40/3,210.15 = 1,215.20/x
3. Step 3: Cross multiply
   2,142.40x = 3,210.15 × 1,215.20
4. Step 4: Simplify right side
   2,142.40x = 3,900,974.28
5. Step 5: Solve for x
   x = 3,900,974.28/2,142.40
6. Step 6: Final answer
   x = 1,820.84