Finding the Fourth Proportional to 1,015.85, 1,401.30 and 642.69

Step by Step Solution

1. Step 1: Write the proportion equation
   1,015.85 : 1,401.30 = 642.69 : x
2. Step 2: Convert to fraction form
   1,015.85/1,401.30 = 642.69/x
3. Step 3: Cross multiply
   1,015.85x = 1,401.30 × 642.69
4. Step 4: Simplify right side
   1,015.85x = 900,601.50
5. Step 5: Solve for x
   x = 900,601.50/1,015.85
6. Step 6: Final answer
   x = 886.55