Finding the Fourth Proportional to 1,388.16, 1,913.76 and 1,138.32

Step by Step Solution

1. Step 1: Write the proportion equation
   1,388.16 : 1,913.76 = 1,138.32 : x
2. Step 2: Convert to fraction form
   1,388.16/1,913.76 = 1,138.32/x
3. Step 3: Cross multiply
   1,388.16x = 1,913.76 × 1,138.32
4. Step 4: Simplify right side
   1,388.16x = 2,178,471.28
5. Step 5: Solve for x
   x = 2,178,471.28/1,388.16
6. Step 6: Final answer
   x = 1,569.32