Finding the Fourth Proportional to 2,620, 3,929.72 and 771.12

Step by Step Solution

1. Step 1: Write the proportion equation
   2,620 : 3,929.72 = 771.12 : x
2. Step 2: Convert to fraction form
   2,620/3,929.72 = 771.12/x
3. Step 3: Cross multiply
   2,620x = 3,929.72 × 771.12
4. Step 4: Simplify right side
   2,620x = 3,030,285.69
5. Step 5: Solve for x
   x = 3,030,285.69/2,620
6. Step 6: Final answer
   x = 1,156.60