Finding the Fourth Proportional to 1,780.31, 2,457.72 and 1,221

Step by Step Solution

1. Step 1: Write the proportion equation
   1,780.31 : 2,457.72 = 1,221 : x
2. Step 2: Convert to fraction form
   1,780.31/2,457.72 = 1,221/x
3. Step 3: Cross multiply
   1,780.31x = 2,457.72 × 1,221
4. Step 4: Simplify right side
   1,780.31x = 3,000,876.12
5. Step 5: Solve for x
   x = 3,000,876.12/1,780.31
6. Step 6: Final answer
   x = 1,685.60