I'm kind of impressed it was able to do basic math even if the reasoning isn't correct. That seems like an impressive emergent behavior for a small cheap model like this.
Interestingly Llama2:13b objects that there is no discount until I clarify: "the discount you're getting [with 2 apples]"
It's not just math though it's any kind of complex reasoning and ambiguity. Comparing to humans is always complex, but humans for the most part wouldn't balk at me asking what discount you're getting without specifying that it's the 2 apples that have the discount in this example. A more advanced model often states the assumptions.
There are lots of nuances in this question as well. I'm still paying 80c more than buying one apple, so I should only buy two apples if I would use two apples.