Q. A test tube floats in water with a small coin at its bottom.The mass of this test tube is equal to mass of seven coins and the external volume is 16 cm cube. It just sinks when the third coin is added.Calculate the mass of each coin.(Density of water=1 gm/cm cube) ( pls explain the answer!) thank you!

Condition to just sink:Letm=mass of each coind=density of waterV=volume of test tubeWeight of test tube + 3 coins = Buoyant forceWeight of test tube + 3 coins = Weight of water displaced by test tube7mg+ 3mg = Vdg10mg=Vdg10m=Vdm=Vd10    =16×110    =1.6 grams

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Because the densities are change in terms of test tube and coin.
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