Finding the Fourth Proportional to 1,112.15, 1,666.20 and 678.80

Step by Step Solution

1. Step 1: Write the proportion equation
   1,112.15 : 1,666.20 = 678.80 : x
2. Step 2: Convert to fraction form
   1,112.15/1,666.20 = 678.80/x
3. Step 3: Cross multiply
   1,112.15x = 1,666.20 × 678.80
4. Step 4: Simplify right side
   1,112.15x = 1,131,016.56
5. Step 5: Solve for x
   x = 1,131,016.56/1,112.15
6. Step 6: Final answer
   x = 1,016.96