Finding the Fourth Proportional to 1,111.40, 1,533.72 and 639.30

Step by Step Solution

1. Step 1: Write the proportion equation
   1,111.40 : 1,533.72 = 639.30 : x
2. Step 2: Convert to fraction form
   1,111.40/1,533.72 = 639.30/x
3. Step 3: Cross multiply
   1,111.40x = 1,533.72 × 639.30
4. Step 4: Simplify right side
   1,111.40x = 980,507.20
5. Step 5: Solve for x
   x = 980,507.20/1,111.40
6. Step 6: Final answer
   x = 882.23