Finding the Fourth Proportional to 1,111.32, 1,533.60 and 639.21

Step by Step Solution

1. Step 1: Write the proportion equation
   1,111.32 : 1,533.60 = 639.21 : x
2. Step 2: Convert to fraction form
   1,111.32/1,533.60 = 639.21/x
3. Step 3: Cross multiply
   1,111.32x = 1,533.60 × 639.21
4. Step 4: Simplify right side
   1,111.32x = 980,292.46
5. Step 5: Solve for x
   x = 980,292.46/1,111.32
6. Step 6: Final answer
   x = 882.10