Finding the Fourth Proportional to 1,421.66, 1,961.72 and 831.78

Step by Step Solution

1. Step 1: Write the proportion equation
   1,421.66 : 1,961.72 = 831.78 : x
2. Step 2: Convert to fraction form
   1,421.66/1,961.72 = 831.78/x
3. Step 3: Cross multiply
   1,421.66x = 1,961.72 × 831.78
4. Step 4: Simplify right side
   1,421.66x = 1,631,719.46
5. Step 5: Solve for x
   x = 1,631,719.46/1,421.66
6. Step 6: Final answer
   x = 1,147.76