Afruit recipe requires 2 apples and 3 mangoes. a baker has 37 mangoes. what is the smallest number of apples he will need to bake as many fruit tarts as possible?

With 37 mangoes you can bake 12 fruit tarts, because you need 3 mangoes for each tarts and you'll use mangoes. The remaining mango is not enough for another tart.

On the other hand, in order to bake 12 tarts, you'll need 24 apples, because you need 2 apples per tart.

So, with 12 apples and 37 mangoes you can bake 12 tart, with one mango as leftover.