Finding the Fourth Proportional to 1,385.20, 1,910.72 and 992.80

Step by Step Solution

1. Step 1: Write the proportion equation
   1,385.20 : 1,910.72 = 992.80 : x
2. Step 2: Convert to fraction form
   1,385.20/1,910.72 = 992.80/x
3. Step 3: Cross multiply
   1,385.20x = 1,910.72 × 992.80
4. Step 4: Simplify right side
   1,385.20x = 1,896,962.82
5. Step 5: Solve for x
   x = 1,896,962.82/1,385.20
6. Step 6: Final answer
   x = 1,369.45