Finding the Fourth Proportional to 1,111.78, 1,534.41 and 639.75

Step by Step Solution

1. Step 1: Write the proportion equation
   1,111.78 : 1,534.41 = 639.75 : x
2. Step 2: Convert to fraction form
   1,111.78/1,534.41 = 639.75/x
3. Step 3: Cross multiply
   1,111.78x = 1,534.41 × 639.75
4. Step 4: Simplify right side
   1,111.78x = 981,638.80
5. Step 5: Solve for x
   x = 981,638.80/1,111.78
6. Step 6: Final answer
   x = 882.94