Finding the Fourth Proportional to 1,421.41, 1,960.80 and 978.55

Step by Step Solution

1. Step 1: Write the proportion equation
   1,421.41 : 1,960.80 = 978.55 : x
2. Step 2: Convert to fraction form
   1,421.41/1,960.80 = 978.55/x
3. Step 3: Cross multiply
   1,421.41x = 1,960.80 × 978.55
4. Step 4: Simplify right side
   1,421.41x = 1,918,726.14
5. Step 5: Solve for x
   x = 1,918,726.14/1,421.41
6. Step 6: Final answer
   x = 1,349.88