Finding the Fourth Proportional to 1,018.61, 1,405.72 and 645.76

Step by Step Solution

1. Step 1: Write the proportion equation
   1,018.61 : 1,405.72 = 645.76 : x
2. Step 2: Convert to fraction form
   1,018.61/1,405.72 = 645.76/x
3. Step 3: Cross multiply
   1,018.61x = 1,405.72 × 645.76
4. Step 4: Simplify right side
   1,018.61x = 907,757.75
5. Step 5: Solve for x
   x = 907,757.75/1,018.61
6. Step 6: Final answer
   x = 891.17