Finding the Fourth Proportional to 1,187.22, 1,781.59 and 639.78

Step by Step Solution

1. Step 1: Write the proportion equation
   1,187.22 : 1,781.59 = 639.78 : x
2. Step 2: Convert to fraction form
   1,187.22/1,781.59 = 639.78/x
3. Step 3: Cross multiply
   1,187.22x = 1,781.59 × 639.78
4. Step 4: Simplify right side
   1,187.22x = 1,139,826.45
5. Step 5: Solve for x
   x = 1,139,826.45/1,187.22
6. Step 6: Final answer
   x = 960.08