Finding the Fourth Proportional to 978.72, 1,349.67 and 839.31

Step by Step Solution

1. Step 1: Write the proportion equation
   978.72 : 1,349.67 = 839.31 : x
2. Step 2: Convert to fraction form
   978.72/1,349.67 = 839.31/x
3. Step 3: Cross multiply
   978.72x = 1,349.67 × 839.31
4. Step 4: Simplify right side
   978.72x = 1,132,791.53
5. Step 5: Solve for x
   x = 1,132,791.53/978.72
6. Step 6: Final answer
   x = 1,157.42