Finding the Fourth Proportional to 1,388.84, 1,914.59 and 990.21

Step by Step Solution

1. Step 1: Write the proportion equation
   1,388.84 : 1,914.59 = 990.21 : x
2. Step 2: Convert to fraction form
   1,388.84/1,914.59 = 990.21/x
3. Step 3: Cross multiply
   1,388.84x = 1,914.59 × 990.21
4. Step 4: Simplify right side
   1,388.84x = 1,895,841.21
5. Step 5: Solve for x
   x = 1,895,841.21/1,388.84
6. Step 6: Final answer
   x = 1,365.06