21.A cubical block of wood of specific gravity 0.5 and chunk of concrete of specific gravity 2.5 are fastened together. The ratio of the mass of wood to the mass of concrete which makes the combination to float with its entire volume submerged under water is

22.The volume of an air bubble rises to three times as it ascends from the bottom of the lake to its surface. Assuming the atmospheric pressure to be 75 cm of Hg and density of water to be 1 / 10 th of the density of mercury, the depth of the lake is

23.A piece of solid weighs 120 g in air, 80 g in water and 60 g in a liquid, then the relative density of the solid, and that of liquid are

24.A body weighs 160 g in air, 130 g in water and 136 g in oil. The specific gravity of oil is

25.A cubical box of wood of side 30 cm weighing 21.6 kg floats on water with two faces horizontal. The depth of immersion of the box is