Final answer:
To get 10 magazines for free, you would need to buy a total of 5 magazines.
Step-by-step explanation:
To get 10 magazines for free, you would need to buy 5 sets of magazines. Each set consists of 3 magazines, for which you would get 2 for free. So, for each set, you would be buying 1 magazine.
Therefore, to get 10 magazines for free, you would need to buy a total of 5 magazines.