Finding the Fourth Proportional to 1,128.69, 1,693.05 and 780.12

Step by Step Solution

1. Step 1: Write the proportion equation
   1,128.69 : 1,693.05 = 780.12 : x
2. Step 2: Convert to fraction form
   1,128.69/1,693.05 = 780.12/x
3. Step 3: Cross multiply
   1,128.69x = 1,693.05 × 780.12
4. Step 4: Simplify right side
   1,128.69x = 1,320,782.17
5. Step 5: Solve for x
   x = 1,320,782.17/1,128.69
6. Step 6: Final answer
   x = 1,170.19