Finding the Fourth Proportional to 1,389.75, 1,918.13 and 830.31

Step by Step Solution

1. Step 1: Write the proportion equation
   1,389.75 : 1,918.13 = 830.31 : x
2. Step 2: Convert to fraction form
   1,389.75/1,918.13 = 830.31/x
3. Step 3: Cross multiply
   1,389.75x = 1,918.13 × 830.31
4. Step 4: Simplify right side
   1,389.75x = 1,592,638.37
5. Step 5: Solve for x
   x = 1,592,638.37/1,389.75
6. Step 6: Final answer
   x = 1,145.99