Finding the Fourth Proportional to 78.60, 117.80 and 42.50

Step by Step Solution

1. Step 1: Write the proportion equation
   78.60 : 117.80 = 42.50 : x
2. Step 2: Convert to fraction form
   78.60/117.80 = 42.50/x
3. Step 3: Cross multiply
   78.60x = 117.80 × 42.50
4. Step 4: Simplify right side
   78.60x = 5,006.50
5. Step 5: Solve for x
   x = 5,006.50/78.60
6. Step 6: Final answer
   x = 63.70