Explanation:

- The sum of the five numbers is given as 1315.

- The average of the first two numbers is 270. So, their sum is $270\times 2=540$.

- The average of the last two numbers is 247.5. So, their sum is $247.5\times 2=495$.

- To find the third number, subtract the sum of the first two and last two numbers from the total sum:

$$\text{Third number}=1315-(540+495)=280$$

- From the given options, the third number, 280, matches option 4.

Here’s the correct answer:

- Option 1: 270

- Option 2: 285

- Option 3: 260

- Option 4: 280

- Option 5: None of these