Finding the Fourth Proportional to 1,640.89, 2,264.90 and 978.20

Step by Step Solution

1. Step 1: Write the proportion equation
   1,640.89 : 2,264.90 = 978.20 : x
2. Step 2: Convert to fraction form
   1,640.89/2,264.90 = 978.20/x
3. Step 3: Cross multiply
   1,640.89x = 2,264.90 × 978.20
4. Step 4: Simplify right side
   1,640.89x = 2,215,525.18
5. Step 5: Solve for x
   x = 2,215,525.18/1,640.89
6. Step 6: Final answer
   x = 1,350.20