Finding the Fourth Proportional to 3,786.21, 5,679.72 and 1,287.90

Step by Step Solution

1. Step 1: Write the proportion equation
   3,786.21 : 5,679.72 = 1,287.90 : x
2. Step 2: Convert to fraction form
   3,786.21/5,679.72 = 1,287.90/x
3. Step 3: Cross multiply
   3,786.21x = 5,679.72 × 1,287.90
4. Step 4: Simplify right side
   3,786.21x = 7,314,911.39
5. Step 5: Solve for x
   x = 7,314,911.39/3,786.21
6. Step 6: Final answer
   x = 1,931.99