Finding the Fourth Proportional to 1,005.51, 1,506.72 and 639.18

Step by Step Solution

1. Step 1: Write the proportion equation
   1,005.51 : 1,506.72 = 639.18 : x
2. Step 2: Convert to fraction form
   1,005.51/1,506.72 = 639.18/x
3. Step 3: Cross multiply
   1,005.51x = 1,506.72 × 639.18
4. Step 4: Simplify right side
   1,005.51x = 963,065.29
5. Step 5: Solve for x
   x = 963,065.29/1,005.51
6. Step 6: Final answer
   x = 957.79