Finding the Fourth Proportional to 1,218.72, 1,681.88 and 666.72

Step by Step Solution

1. Step 1: Write the proportion equation
   1,218.72 : 1,681.88 = 666.72 : x
2. Step 2: Convert to fraction form
   1,218.72/1,681.88 = 666.72/x
3. Step 3: Cross multiply
   1,218.72x = 1,681.88 × 666.72
4. Step 4: Simplify right side
   1,218.72x = 1,121,343.03
5. Step 5: Solve for x
   x = 1,121,343.03/1,218.72
6. Step 6: Final answer
   x = 920.10