Multiple choice

Directions: Select the correct alternative from the given choices. The density of a liquid is defined as the mass per unit volume of the liquid. The densities of two liquids A and B, are in the ratio 2 : 1. 70 kg of liquid A is mixed with 30 kg of liquid of B to form a mixture. ln this mixture, liquid B evaporates at a rate (in kg/hr) which is twice as fast compared to that of liquid A, which evaporates at a rate of 1 kg/hour. Find the number of hours for which the mixture needs to be evaporated, for the density of the resultant mixture to become 1.04 times that of the original mixture (i.e., before evaporation).

  1. 2.5

  2. 3

  3. 3.5

  4. 4
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Let the density of B be d, so the density of A is 2d. Initially, the mixture has volume 70/(2d) + 30/d = 65/d. After t hours, its mass is 100 - 3t and volume is (65 - 2.5t)/d; setting the density ratio to 1.04 gives t = 4 hours.

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