When do you know to use 入れます(いれます) versus 置きます(おきます)? Is 入れます for putting something inside something else?
Yeah. 置く means to place something on.
Why is "I put the cup into the box." wrong?
Well, we know what's in the box now
I really hope Duo gives us a sentence that reads "Put the lime in the coconut."
there's no plural in japanese. how do I know if it's a cup or cups?
You could give the quantity if it was really important. By the way, what's the counter for empty cups?
Is there any reason this can't be translated as "I put the cup on the box."
Oops. Because it is「入れます」 not「置ます」