Mass of each coin, m=2g Mass of 4 coin =4×m M′=4×2⇒M′=8g Let mass of the metre stick be m. The centre of mass lies at its mid-point i.e at the mark of 50cm When the coins are placed 10cm away from the end B, the centre of mass gets shifted by 4cm from point G towards the coins side. Now, using the principle of moment about point P, we get 8g(46−10)−mg(50−46)=0 8×36−m×4=0 m=