Finding the Fourth Proportional to 1,139.12, 1,571.60 and 641.70

Step by Step Solution

1. Step 1: Write the proportion equation
   1,139.12 : 1,571.60 = 641.70 : x
2. Step 2: Convert to fraction form
   1,139.12/1,571.60 = 641.70/x
3. Step 3: Cross multiply
   1,139.12x = 1,571.60 × 641.70
4. Step 4: Simplify right side
   1,139.12x = 1,008,495.72
5. Step 5: Solve for x
   x = 1,008,495.72/1,139.12
6. Step 6: Final answer
   x = 885.33