Finding the Fourth Proportional to 1,156.08, 1,731.72 and 642

Step by Step Solution

1. Step 1: Write the proportion equation
   1,156.08 : 1,731.72 = 642 : x
2. Step 2: Convert to fraction form
   1,156.08/1,731.72 = 642/x
3. Step 3: Cross multiply
   1,156.08x = 1,731.72 × 642
4. Step 4: Simplify right side
   1,156.08x = 1,111,764.24
5. Step 5: Solve for x
   x = 1,111,764.24/1,156.08
6. Step 6: Final answer
   x = 961.67