What volume of 75% alcohol by weight (d=0.80g/cm3) must be used to prepare 150cm3 of 30% alcohol by weight (d=0.90g/cm3)?

As par question mass of alcohol is same in both solutions. Consider V ml of alcohol required.

Then 

75​/100×0.8×V=30/100 ×0.9×150

V=67.5mL

ILLUSTRATIVE EXAMPLES:

(1):Calculate the mole fraction of solute in the 12 molal aqueous solution of CaCO3.

(2):The mole fraction of glucose in aqueous solution is 0.2 , The molality of solution will be.

(3):If the mole fraction of a solute is changed from 1/4 to 1/2 in the 800 gm of solvent . then the ratio of molality will be .

(4):Mole fraction of I2 (iodine) in benzene (C6H6) is 0.2 . Calculate the molality of iodine (I2) in benzene.

(5):Calculate the amount of water that should be added to 16 gm methanol to make mole fraction of methanol as 0.25.?