I did a cardio session of/for fifteen minutes

[tufguy]

1) I did a cardio session of fifteen minutes.
2) I did a cardio session for fifteen minutes.

Please check my sentences. I often get confused between "of" and "for" in these kinds of sentences. I would like to know what is the way to know where we have to use "of" and where we have to use "for" or are these sometimes interchangeable?

 

[emsr2d2]

1) I did a cardio session of fifteen minutes.
2) I did a cardio session for fifteen minutes.

Please check my sentences. I often get confused between "of" and "for" in these kinds of sentences. I would like to know what is the way how to know where we have to use "of" and where we have to use "for", or are these sometimes interchangeable?

Both sentences are grammatically correct and possible. In the first, "of fifteen minutes" is used to describe the duration of the cardio session. In the second, "for fifteen minutes" is used to express exactly how long you did the cardio session for.

 

[SoothingDave]

A "cardio session of 15 minutes" is better.

Or, "I did cardio for 15 minutes."