Finding the Fourth Proportional to 1,421.79, 1,961.31 and 978.92

Step by Step Solution

1. Step 1: Write the proportion equation
   1,421.79 : 1,961.31 = 978.92 : x
2. Step 2: Convert to fraction form
   1,421.79/1,961.31 = 978.92/x
3. Step 3: Cross multiply
   1,421.79x = 1,961.31 × 978.92
4. Step 4: Simplify right side
   1,421.79x = 1,919,965.59
5. Step 5: Solve for x
   x = 1,919,965.59/1,421.79
6. Step 6: Final answer
   x = 1,350.39