You lose weight when you remain calorie deficit i.e. you burn more calories in a day than what you eat. You burn calories both by running as well as weight training. On an average an 80 kg person would burn around 675 calories running at 8kmph for an hour while same person burns around 280 calories in gym in an hour. However, weight training helps you to gain muscles which would make you burn more calories throughout the day. It’s because muscles consume more calories to sustain. Therefore, it is recommended to mix both for better results.