Finding the Fourth Proportional to 1,008.06, 1,388.50 and 712.80

Step by Step Solution

1. Step 1: Write the proportion equation
   1,008.06 : 1,388.50 = 712.80 : x
2. Step 2: Convert to fraction form
   1,008.06/1,388.50 = 712.80/x
3. Step 3: Cross multiply
   1,008.06x = 1,388.50 × 712.80
4. Step 4: Simplify right side
   1,008.06x = 989,722.80
5. Step 5: Solve for x
   x = 989,722.80/1,008.06
6. Step 6: Final answer
   x = 981.81