Finding the Fourth Proportional to 978.69, 1,470.91 and 815.21

Step by Step Solution

1. Step 1: Write the proportion equation
   978.69 : 1,470.91 = 815.21 : x
2. Step 2: Convert to fraction form
   978.69/1,470.91 = 815.21/x
3. Step 3: Cross multiply
   978.69x = 1,470.91 × 815.21
4. Step 4: Simplify right side
   978.69x = 1,199,100.54
5. Step 5: Solve for x
   x = 1,199,100.54/978.69
6. Step 6: Final answer
   x = 1,225.21