Actually, in this case it doesn't matter where "le" is placed. It still expresses the same idea. Generally speaking, "le" is placed *after* the verb when marking a completed action. 我喝了三杯咖啡。- I drank three cups of coffee. However, sometimes you'll see the sentence order worded differently when asking questions. 你门票买了吗？did you buy the entrance ticket?-here, the verb is placed after the object, so "le" is placed towards the end of the sentence. It's also correct to ask: 你买了门票吗？- but the first way is probably more common. 了 does not have any particular meaning, so it really depends on the sentence. Many times when 了is at the end of a sentence, it implies a change. 我吃饱了. - I'm full [after eating a meal as opposed to before] 下雨了 - it's raining[now] Or take this scenario where you buy a milkshake and two cookies. Once the lady behind the counter brings you your drink she asks: 还要什么？-do you want anything else? Since you have bought everything you wanted, you would then respond:不要了-no[not anymore;I'm satisfied] 不要 alone would mean "doesn't want" but here 了 implies 'not anymore' since there isn't an exact word to express that in Mandarin.

You have to know what

ping is right

I think they are the same meaning. But we are used to use the first one.