1. The problem states that Isaac and his grandma use 16 peaches to make cobbler and have 24 peaches left to make pies. 2. We need to find the total number of peaches they bought. Let the total number of peaches be $x$. 3. According to the problem, the peaches used for cobbler plus the peaches left for pies equals the total peaches: $$16 + 24 = x$$ 4. Simplify the right side: $$16 + 24 = 40$$ 5. Therefore, the total number of peaches is: $$x = 40$$ 6. Isaac and his grandma bought 40 peaches in total.