Finding the Fourth Proportional to 1,200.71, 1,800.72 and 420.57

Step by Step Solution

1. Step 1: Write the proportion equation
   1,200.71 : 1,800.72 = 420.57 : x
2. Step 2: Convert to fraction form
   1,200.71/1,800.72 = 420.57/x
3. Step 3: Cross multiply
   1,200.71x = 1,800.72 × 420.57
4. Step 4: Simplify right side
   1,200.71x = 757,326.71
5. Step 5: Solve for x
   x = 757,326.71/1,200.71
6. Step 6: Final answer
   x = 630.73