If a balloon filled with helium weighs 21.6 kg, knowing that helium's density is 0.18 kg/m3 then what is its volume?

120 m³

Explanation:

Density is defined as the mass per unit volume. It is an intensive property,

in  mathematically defined as mass divided by volume:

Density = mass /Volume

Volume = Mass / Density

Volume = 21.6 kg / 0.18 kg/m³

              = 120 m³

answer: at 24 february, 2014 the population gets twice of its initial population.

explanation:

since we have given that

the population for alpha city, t years after january 1, 2004 is given as

first we find out the initial population, i.e. t=0,

so, our quadratic equation becomes,

according to question, we have said that if the population has twice its initial population, then it becomes

so, time taken to reach this above mentioned population is given by

now, we know that time can't be negative so, we take t=9.149 years.

hence, at 24 february, 2014 the population gets twice of its initial population.