Finding the Fourth Proportional to 1,015.76, 1,401.89 and 642.71

Step by Step Solution

1. Step 1: Write the proportion equation
   1,015.76 : 1,401.89 = 642.71 : x
2. Step 2: Convert to fraction form
   1,015.76/1,401.89 = 642.71/x
3. Step 3: Cross multiply
   1,015.76x = 1,401.89 × 642.71
4. Step 4: Simplify right side
   1,015.76x = 901,009.01
5. Step 5: Solve for x
   x = 901,009.01/1,015.76
6. Step 6: Final answer
   x = 887.03