Finding the Fourth Proportional to 1,389.70, 1,916.96 and 917.61

Step by Step Solution

1. Step 1: Write the proportion equation
   1,389.70 : 1,916.96 = 917.61 : x
2. Step 2: Convert to fraction form
   1,389.70/1,916.96 = 917.61/x
3. Step 3: Cross multiply
   1,389.70x = 1,916.96 × 917.61
4. Step 4: Simplify right side
   1,389.70x = 1,759,009.89
5. Step 5: Solve for x
   x = 1,759,009.89/1,389.70
6. Step 6: Final answer
   x = 1,265.75