Finding the Fourth Proportional to 86.72, 129.38 and 83.70

Step by Step Solution

1. Step 1: Write the proportion equation
   86.72 : 129.38 = 83.70 : x
2. Step 2: Convert to fraction form
   86.72/129.38 = 83.70/x
3. Step 3: Cross multiply
   86.72x = 129.38 × 83.70
4. Step 4: Simplify right side
   86.72x = 10,828.69
5. Step 5: Solve for x
   x = 10,828.69/86.72
6. Step 6: Final answer
   x = 124.88