Half life \\\\( = 10min = \\dfrac {ln2}{\\lambda}\\\\)Nuclei disintegrate = 450Nuclei left = 600-450 =150\\\\(N=N_{o}e^{-\\lambda}{t}\\\\)\\\\(150 = 600 e^{\\dfrac{-ln2}{10} t}\\\\)so, t = 20 minutes