Finding the Fourth Proportional to 1,030.56, 1,421.20 and 978.72

Step by Step Solution

1. Step 1: Write the proportion equation
   1,030.56 : 1,421.20 = 978.72 : x
2. Step 2: Convert to fraction form
   1,030.56/1,421.20 = 978.72/x
3. Step 3: Cross multiply
   1,030.56x = 1,421.20 × 978.72
4. Step 4: Simplify right side
   1,030.56x = 1,390,956.86
5. Step 5: Solve for x
   x = 1,390,956.86/1,030.56
6. Step 6: Final answer
   x = 1,349.71