Finding the Fourth Proportional to 1,290.63, 1,780.59 and 766.65

Step by Step Solution

1. Step 1: Write the proportion equation
   1,290.63 : 1,780.59 = 766.65 : x
2. Step 2: Convert to fraction form
   1,290.63/1,780.59 = 766.65/x
3. Step 3: Cross multiply
   1,290.63x = 1,780.59 × 766.65
4. Step 4: Simplify right side
   1,290.63x = 1,365,089.32
5. Step 5: Solve for x
   x = 1,365,089.32/1,290.63
6. Step 6: Final answer
   x = 1,057.69