Finding the Fourth Proportional to 1,131.78, 1,561.80 and 666

Step by Step Solution

1. Step 1: Write the proportion equation
   1,131.78 : 1,561.80 = 666 : x
2. Step 2: Convert to fraction form
   1,131.78/1,561.80 = 666/x
3. Step 3: Cross multiply
   1,131.78x = 1,561.80 × 666
4. Step 4: Simplify right side
   1,131.78x = 1,040,158.80
5. Step 5: Solve for x
   x = 1,040,158.80/1,131.78
6. Step 6: Final answer
   x = 919.05