Finding the Fourth Proportional to 78.86, 108.78 and 71.57

Step by Step Solution

1. Step 1: Write the proportion equation
   78.86 : 108.78 = 71.57 : x
2. Step 2: Convert to fraction form
   78.86/108.78 = 71.57/x
3. Step 3: Cross multiply
   78.86x = 108.78 × 71.57
4. Step 4: Simplify right side
   78.86x = 7,784.84
5. Step 5: Solve for x
   x = 7,784.84/78.86
6. Step 6: Final answer
   x = 98.72