To obtain a two times magnified real image in front of a concave mirror of focal length 20 cm, the object should be placed at a specific distance from the mirror.

Here are the steps to determine the position of the object:

1. Understand the concept of magnification: Magnification is the ratio of the height of the image to the height of the object. In this case, the magnification is given as 2.

2. Use the mirror formula: The mirror formula is 1/f = 1/v + 1/u, where f is the focal length, v is the image distance, and u is the object distance. We know that the image is real, so v is negative.

3. Use the magnification formula: The magnification formula is m = -v/u, where m is the magnification.

4. Substitute the given values: We know that the focal length is 20 cm, and the magnification is 2. We can use these values to find u.

5. Solve for u: Substituting the values in the magnification formula, we get:

2 = -v/u

v = -2u

Substituting v in the mirror formula, we get:

1/20 = 1/-2u + 1/u

1/20 = -1/u

u = -20 cm

Since u is negative, it means that the object should be placed 20 cm in front of the mirror.

Therefore, the object should be placed 20 cm in front of the concave mirror of focal length 20 cm to obtain a two times magnified real image.