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1. Teaching this lesson was of 15 minutes' duration.

2. I taught this lesson for a 15 minute period.

3. I taught this lesson for a period of 15 minutes.

4. I taught this lesson of15 minutes' duration.

Please correct the sentences.

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1. Teaching this lesson was of 15 minutes' duration. No, say instead

eg Teaching this lesson took 15 minutes,

2. I taught this lesson for a 15-minute period. OK

3. I taught this lesson for a period of 15 minutes. OK

4. I taught this lesson of15 minutes' duration.

Please correct the sentences. No, say instead

eg It took me 15 minutes to teach this lesson.

Clive

(We sometimes say 'a quarter of an hour.)