Finding the Fourth Proportional to 100.51, 138.72 and 86.83

Step by Step Solution

1. Step 1: Write the proportion equation
   100.51 : 138.72 = 86.83 : x
2. Step 2: Convert to fraction form
   100.51/138.72 = 86.83/x
3. Step 3: Cross multiply
   100.51x = 138.72 × 86.83
4. Step 4: Simplify right side
   100.51x = 12,045.06
5. Step 5: Solve for x
   x = 12,045.06/100.51
6. Step 6: Final answer
   x = 119.84