Learn English – “Short delivery time” vs “fast delivery time”

Ten percent of the time does not mean ten percent of the times.

If you read it as once out of ten times, then what are those "times"?

What the sentence says is that it's all right to be sad for ten percent of all the time you spend during a day, or your life, or whatever.

So that could be:

• 1 hour in a 10-hour period, or
• 2 hours and 24 minutes in a day, or
• 6 minutes per hour, or
• 1 year in ten, or
• 8 years in an average lifetime of 80 years

Well, actually, it is unlikely that a precise 10% is meant - ten percent of the time basically means that it is all right to be sad every now and again, as long as it doesn't become too much; 50% would mean you are sad half the time, or 100% that you are always sad, and that probably is not good for you.

So yes, your interpretation of the meaning was correct.

Person 2 is being dreadfully picky in my opinion. For one, to say that something "sounds very ghetto" as a negative is pretty insulting to anyone who lives in a ghetto. There are certain racial and social undercurrents to this statement that are far too complex to go into here as well. To get an idea for yourself, google "ghetto speech" and you will see a wide range of interesting material, as well as a good deal of hateful and racist commentary.

Suffice it to say that "where is it at?" as opposed to "where is it?" is somewhat "slangy" but also commonly used, at least in American English. Whether or not it is technically grammatically incorrect, it is common enough that most people just don't care.

Also, the informal idiom where it's at generally means a fashionable place where the most interesting things are happening at present. By extension, it can be used to refer to people, things or activities as well:

Studio 54 is where it's at.
Whole wheat spaghetti is where it's at.
Kant's Critique of Pure Reason is where it's at.

And so on.