Finding the Fourth Proportional to 1,390.21, 2,086.74 and 931.20

Step by Step Solution

1. Step 1: Write the proportion equation
   1,390.21 : 2,086.74 = 931.20 : x
2. Step 2: Convert to fraction form
   1,390.21/2,086.74 = 931.20/x
3. Step 3: Cross multiply
   1,390.21x = 2,086.74 × 931.20
4. Step 4: Simplify right side
   1,390.21x = 1,943,167.95
5. Step 5: Solve for x
   x = 1,943,167.95/1,390.21
6. Step 6: Final answer
   x = 1,397.75