Finding the Fourth Proportional to 1,420.72, 1,960.68 and 831.40

Step by Step Solution

1. Step 1: Write the proportion equation
   1,420.72 : 1,960.68 = 831.40 : x
2. Step 2: Convert to fraction form
   1,420.72/1,960.68 = 831.40/x
3. Step 3: Cross multiply
   1,420.72x = 1,960.68 × 831.40
4. Step 4: Simplify right side
   1,420.72x = 1,630,109.35
5. Step 5: Solve for x
   x = 1,630,109.35/1,420.72
6. Step 6: Final answer
   x = 1,147.38