You buy two t-shirts and i say oh you pay the full price of $12 for the first t-shirt and you get the second t-shirt for have this price what fraction of the full price do you pay for two shirts

You paid 3/4 of the full price.

Explanation: Total cost of the two shirts = shirt one ($12) + shirt two (half price, so $6) or $18 all together. If you had paid full price for both shirts, it would have cost you $24, or $12 times 2. 24 - 18 = 6, so you saved six dollars. 24 (full price) divided by 6 = 4, so we know that $6 is 1/4 of the full price. Because of this, we know that the amount you spent ($18) was 3/4 of the full price, since 4/4 (total) - 1/4 (amount saved) = 3/4 (amount spent). Another way to solve this is to simply divide 18 by 24.