Explanation:

- The mean of p, q, r, s, and t is 280. This means the sum of these five numbers is 280 * 5 = 1400.

- The mean of p, r, and t is 240, meaning their sum is 240 * 3 = 720.

- We need to find the mean of q and s. To do this, subtract the sum of p, r, and t from the total sum: 1400 - 720 = 680.

- The mean of q and s will be 680 divided by 2, since there are two numbers: 680 / 2 = 340.

- Option 4: 340 is the correct answer.

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