What is the average amount of sit ups should a ten year old girl be able to do in a minute?

If you're thirteen then the chance of getting a six-pack is very slight. Six-packs don't just come from sit-ups, they also require a rather active lifestyle, and a healthy diet of course. A good number of sit-ups is about 250-300 a day. If you do this everyday - and not in sets, has to be 300 without too much of a rest - then you should have a six-pack within about 4 or 5 weeks. This is assuming you are already exceptionally fit, and very active, and have a good diet, as mentioned before. For an alternative do about 200 crunches a day instead of sit-ups. Crunches involve coming up halfway, or to the point where it hurts, and holding for three seconds. Then go down, rest for two seconds, and repeat. To get the six-pack even faster hold your stomach in, or flex your stomach muscles, all the time. When I say hold you stomach in I am in no way meaning all the way in so it looks abnormal, I merely mean suck it in to the point where it hurts. Getting a six-pack is hard, and does hurt, a lot. I hope this helps, but since you're only 13 you don't need to worry so much about the six-pack. It's much better to be extremely fit, and have e good body overall, not just a six-pack...