Finding the Fourth Proportional to 2,105.90, 2,905.80 and 1,221.53

Step by Step Solution

1. Step 1: Write the proportion equation
   2,105.90 : 2,905.80 = 1,221.53 : x
2. Step 2: Convert to fraction form
   2,105.90/2,905.80 = 1,221.53/x
3. Step 3: Cross multiply
   2,105.90x = 2,905.80 × 1,221.53
4. Step 4: Simplify right side
   2,105.90x = 3,549,507.35
5. Step 5: Solve for x
   x = 3,549,507.35/2,105.90
6. Step 6: Final answer
   x = 1,685.51