It is a little strange that "tu" is being used a lot here, when you need to be very careful when to use it ! "tum" would indeed be more helpful. Or even "aap" !
How come "you are eating" (the present particple) is an incorrect translation? How would you say that in Hindi?
No. This is a weird duolingo sentence that is grammatically correct but probably won't find much use in real life.
Let's replace तुम with वह.
वह खाता है। - He eats.
All these are correct.
तुम खाते हो। Tum khaate ho.
तू खाता है। Tu khaata hai.
आप खाते हैं। Aap khaate hain.
I suggest using the last one for formal situations or with the people elder to you and the first one for informal situation or when you are talking to younger people. Avoid the second one as its considered very rude in many states across India.
Exactly. So why is Duo even teaching the second sentence? It is rude in my state and may only be used in conversation with friends (though not true in all friend groups).