Question

A room with poor air quality has a particle concentration of 80 units. ​A fan removes 50% of the remaining particles each hour. What is the ​particle concentration, in these same units, in the room after 2 hours? ​​

Answer 1

20 units

Explanation:

Initial particle concentration = 80 units

Particles removed each hour = 50% of the remaining particles

To find:

Particle concentration after 2 hours = ?

Solution:

Particles removed in 1 hour = 50% of remaining particles

i.e. Particles removed in 1 hour = 50% of initial concentration

Particles removed in 1 hour = 50% of 80 = 40

Particles removed in next 1 hour = 50% of remaining particles

i.e. Particles removed in next 1 hour = 50% of concentration after 1 hour

Particles removed in next 1 hour = 50% of 40 = 20

Total particles concentration removed in 2 hours = 40 + 20 = 60 units

Therefore, particle concentration after 2 hours = Initial concentration - Total particle concentration removed in 2 hours

= 80 - 60 = 20 units