Finding the Fourth Proportional to 1,428.34, 1,971.90 and 931.30

Step by Step Solution

1. Step 1: Write the proportion equation
   1,428.34 : 1,971.90 = 931.30 : x
2. Step 2: Convert to fraction form
   1,428.34/1,971.90 = 931.30/x
3. Step 3: Cross multiply
   1,428.34x = 1,971.90 × 931.30
4. Step 4: Simplify right side
   1,428.34x = 1,836,430.47
5. Step 5: Solve for x
   x = 1,836,430.47/1,428.34
6. Step 6: Final answer
   x = 1,285.71