How can you lose leg fat in 20 days?

This is a very good question. Now please remember it is not recommended to lose more than 10lbs per week, so you're goal is pretty decent.

To lose weight you must first gain weight (Muscle weights more than fat)

Now, on a better note.

Here are some things you can do to eliminate fat from your body, fast.

Stop smoking

Stop drinking alcohol

Stop drinking ANY soda's and just drink milk, water or tea

Those above will show a DRASTIC change in weight within one month.

If you're just focusing on your legs try doing some work outs where all you use it your legs. Try spreading them apart and with some resistance (A ball, some springs or a device for this) squeeze them tight together and hold it.

Walk, don't run. 1 mile a day.

Eat 1 bowl of whole grain cereal a day.

Drink slim-fast, It works.

Hope you got something from this.