In an experiment for determination of the focal length of a thin convex lens, the distance of the object from the lens is \( 10 \pm 0.1 \, \text{cm} \) and the distance of its real image from the lens is \( 20 \pm 0.2 \, \text{cm} \). The error in the determination of focal length of the lens is \( n\% \). The value of \( n \) is __________.
