Finding the Fourth Proportional to 1,938.18, 2,907.72 and 639.78

Step by Step Solution

1. Step 1: Write the proportion equation
   1,938.18 : 2,907.72 = 639.78 : x
2. Step 2: Convert to fraction form
   1,938.18/2,907.72 = 639.78/x
3. Step 3: Cross multiply
   1,938.18x = 2,907.72 × 639.78
4. Step 4: Simplify right side
   1,938.18x = 1,860,301.10
5. Step 5: Solve for x
   x = 1,860,301.10/1,938.18
6. Step 6: Final answer
   x = 959.82