I eat 1200 calories a day and do weight training for an hour , run for 10 min& play tennis , how many calories do I burn

Each person is different. If you have more muscles you may burn more calories. It also depends on the thyroid and how much estrogen is in the body...and fat.

1200 calories sounds way too low - there's a good chance your body is in starvation mode. Check out this site to calculate how many calories your body burns at rest and follow the link to calculate your daily calorie needs: http://www.bmi-calculator.net/bmr-calculator/ The only way to know what you're burning is to use a Heart Rate Monitor or some other calorie monitoring device like a BodyBugg or FitBit.

1200 cals is fairly low. For that to work out, you'd either have to be real tiny, or on a quite strict diet. To survive well on 1200 cal you really need to know what to eat. Weight training isn't particularly effective when it comes to burning calories, you just can't get the consistent and sustained heart rate increase needed for a good burn. I'd say about 300 cals. A 10 minute run isn't much to brag about either. Maybe 100 cals. Tennis - you didn't state how long. If you're really keen on keeping track of the cals - get yourself one of those watch-like heart rate monitors. Most of them have a calorie counting feature as well.

Here is a chart of calories burned/activity. You can get a general idea from this chart.... http://www.nutristrategy.com/activitylist4.htm