Finding the Fourth Proportional to 1,390.78, 1,919.59 and 801.42

Step by Step Solution

1. Step 1: Write the proportion equation
   1,390.78 : 1,919.59 = 801.42 : x
2. Step 2: Convert to fraction form
   1,390.78/1,919.59 = 801.42/x
3. Step 3: Cross multiply
   1,390.78x = 1,919.59 × 801.42
4. Step 4: Simplify right side
   1,390.78x = 1,538,397.82
5. Step 5: Solve for x
   x = 1,538,397.82/1,390.78
6. Step 6: Final answer
   x = 1,106.14