Finding the Fourth Proportional to 91.88, 138.18 and 78.38

Step by Step Solution

1. Step 1: Write the proportion equation
   91.88 : 138.18 = 78.38 : x
2. Step 2: Convert to fraction form
   91.88/138.18 = 78.38/x
3. Step 3: Cross multiply
   91.88x = 138.18 × 78.38
4. Step 4: Simplify right side
   91.88x = 10,830.55
5. Step 5: Solve for x
   x = 10,830.55/91.88
6. Step 6: Final answer
   x = 117.88