Finding the Fourth Proportional to 100.78, 139.05 and 56.53

Step by Step Solution

1. Step 1: Write the proportion equation
   100.78 : 139.05 = 56.53 : x
2. Step 2: Convert to fraction form
   100.78/139.05 = 56.53/x
3. Step 3: Cross multiply
   100.78x = 139.05 × 56.53
4. Step 4: Simplify right side
   100.78x = 7,860.67
5. Step 5: Solve for x
   x = 7,860.67/100.78
6. Step 6: Final answer
   x = 78.00