You can calculate the ratio by adding together the percentage of children (aged under 15 years), and the older population (aged 65+), dividing that percentage by the working-age population (aged 15-64 years), multiplying that percentage by 100 so the ratio is expressed as the number of 'dependents' per 100 people aged
The continental crust is made up of rocks that consist primarily of silica and alumina called the "sial". The next layer of the Earth is called the mantle.
