A number is tripled, then 7 is added to the result, and finally the sum is divided by 2 to get 11. What is the original number?

Work backward through the steps. The final result, 11, came from dividing by 2, so before that the number was $11 \times 2 = 22$. Before adding 7, it was $22 - 7 = 15$. Before tripling, it was $15 \div 3 = 5$. The original number is 5, choice A. Check forward: $5 \times 3 = 15$, $15 + 7 = 22$, and $22 \div 2 = 11$. Choice B (8) comes from forgetting to undo the division by 2 first. Choice C (15) stops before undoing the tripling. Choice D (3) comes from dividing by 3 too early or mishandling the order of operations. Undo in reverse order.