Alike jump roped for 20 mins she stopped at 8:05 when did she start jumping

Subtract twenty minutes. 7:45.

You can also think about it this way to make it easier. If she had started at 8:00, then she had only jump rope for 5 minutes. So 20-5=15. She started jump roping 15 minutes before 8. This is 7:45.

Alike started at 7:45