Finding the Fourth Proportional to 1,389.72, 1,918.12 and 917.70

Step by Step Solution

1. Step 1: Write the proportion equation
   1,389.72 : 1,918.12 = 917.70 : x
2. Step 2: Convert to fraction form
   1,389.72/1,918.12 = 917.70/x
3. Step 3: Cross multiply
   1,389.72x = 1,918.12 × 917.70
4. Step 4: Simplify right side
   1,389.72x = 1,760,258.72
5. Step 5: Solve for x
   x = 1,760,258.72/1,389.72
6. Step 6: Final answer
   x = 1,266.63