Finding the Fourth Proportional to 1,128.37, 1,690.93 and 640.39

Step by Step Solution

1. Step 1: Write the proportion equation
   1,128.37 : 1,690.93 = 640.39 : x
2. Step 2: Convert to fraction form
   1,128.37/1,690.93 = 640.39/x
3. Step 3: Cross multiply
   1,128.37x = 1,690.93 × 640.39
4. Step 4: Simplify right side
   1,128.37x = 1,082,848.83
5. Step 5: Solve for x
   x = 1,082,848.83/1,128.37
6. Step 6: Final answer
   x = 959.66