Finding the Fourth Proportional to 1,290.55, 1,780.30 and 870.37

Step by Step Solution

1. Step 1: Write the proportion equation
   1,290.55 : 1,780.30 = 870.37 : x
2. Step 2: Convert to fraction form
   1,290.55/1,780.30 = 870.37/x
3. Step 3: Cross multiply
   1,290.55x = 1,780.30 × 870.37
4. Step 4: Simplify right side
   1,290.55x = 1,549,519.71
5. Step 5: Solve for x
   x = 1,549,519.71/1,290.55
6. Step 6: Final answer
   x = 1,200.67