Finding the Fourth Proportional to 82.90, 123.75 and 72.15

Step by Step Solution

1. Step 1: Write the proportion equation
   82.90 : 123.75 = 72.15 : x
2. Step 2: Convert to fraction form
   82.90/123.75 = 72.15/x
3. Step 3: Cross multiply
   82.90x = 123.75 × 72.15
4. Step 4: Simplify right side
   82.90x = 8,928.10
5. Step 5: Solve for x
   x = 8,928.10/82.90
6. Step 6: Final answer
   x = 107.70