Finding the Fourth Proportional to 1,015.68, 1,401.86 and 643.15

Step by Step Solution

1. Step 1: Write the proportion equation
   1,015.68 : 1,401.86 = 643.15 : x
2. Step 2: Convert to fraction form
   1,015.68/1,401.86 = 643.15/x
3. Step 3: Cross multiply
   1,015.68x = 1,401.86 × 643.15
4. Step 4: Simplify right side
   1,015.68x = 901,606.26
5. Step 5: Solve for x
   x = 901,606.26/1,015.68
6. Step 6: Final answer
   x = 887.69