Finding the Fourth Proportional to 172.78, 238.42 and 99.10

Step by Step Solution

1. Step 1: Write the proportion equation
   172.78 : 238.42 = 99.10 : x
2. Step 2: Convert to fraction form
   172.78/238.42 = 99.10/x
3. Step 3: Cross multiply
   172.78x = 238.42 × 99.10
4. Step 4: Simplify right side
   172.78x = 23,627.42
5. Step 5: Solve for x
   x = 23,627.42/172.78
6. Step 6: Final answer
   x = 136.75