Finding the Fourth Proportional to 1,018.89, 1,405.52 and 645.21

Step by Step Solution

1. Step 1: Write the proportion equation
   1,018.89 : 1,405.52 = 645.21 : x
2. Step 2: Convert to fraction form
   1,018.89/1,405.52 = 645.21/x
3. Step 3: Cross multiply
   1,018.89x = 1,405.52 × 645.21
4. Step 4: Simplify right side
   1,018.89x = 906,857.17
5. Step 5: Solve for x
   x = 906,857.17/1,018.89
6. Step 6: Final answer
   x = 890.04