Finding the Fourth Proportional to 2,587.78, 3,881.76 and 639.98

Step by Step Solution

1. Step 1: Write the proportion equation
   2,587.78 : 3,881.76 = 639.98 : x
2. Step 2: Convert to fraction form
   2,587.78/3,881.76 = 639.98/x
3. Step 3: Cross multiply
   2,587.78x = 3,881.76 × 639.98
4. Step 4: Simplify right side
   2,587.78x = 2,484,263.35
5. Step 5: Solve for x
   x = 2,484,263.35/2,587.78
6. Step 6: Final answer
   x = 960.00