Finding the Fourth Proportional to 1,388.69, 1,915.77 and 915.98

Step by Step Solution

1. Step 1: Write the proportion equation
   1,388.69 : 1,915.77 = 915.98 : x
2. Step 2: Convert to fraction form
   1,388.69/1,915.77 = 915.98/x
3. Step 3: Cross multiply
   1,388.69x = 1,915.77 × 915.98
4. Step 4: Simplify right side
   1,388.69x = 1,754,792.85
5. Step 5: Solve for x
   x = 1,754,792.85/1,388.69
6. Step 6: Final answer
   x = 1,263.64