Finding the Fourth Proportional to 1,390.80, 1,919.52 and 999.12

Step by Step Solution

1. Step 1: Write the proportion equation
   1,390.80 : 1,919.52 = 999.12 : x
2. Step 2: Convert to fraction form
   1,390.80/1,919.52 = 999.12/x
3. Step 3: Cross multiply
   1,390.80x = 1,919.52 × 999.12
4. Step 4: Simplify right side
   1,390.80x = 1,917,830.82
5. Step 5: Solve for x
   x = 1,917,830.82/1,390.80
6. Step 6: Final answer
   x = 1,378.94