Finding the Fourth Proportional to 1,389.79, 2,085.37 and 659.88

Step by Step Solution

1. Step 1: Write the proportion equation
   1,389.79 : 2,085.37 = 659.88 : x
2. Step 2: Convert to fraction form
   1,389.79/2,085.37 = 659.88/x
3. Step 3: Cross multiply
   1,389.79x = 2,085.37 × 659.88
4. Step 4: Simplify right side
   1,389.79x = 1,376,092.31
5. Step 5: Solve for x
   x = 1,376,092.31/1,389.79
6. Step 6: Final answer
   x = 990.15