Finding the Fourth Proportional to 1,013.75, 1,521.69 and 643.98

Step by Step Solution

1. Step 1: Write the proportion equation
   1,013.75 : 1,521.69 = 643.98 : x
2. Step 2: Convert to fraction form
   1,013.75/1,521.69 = 643.98/x
3. Step 3: Cross multiply
   1,013.75x = 1,521.69 × 643.98
4. Step 4: Simplify right side
   1,013.75x = 979,941.22
5. Step 5: Solve for x
   x = 979,941.22/1,013.75
6. Step 6: Final answer
   x = 966.65