Classroom Activity for the NOVA program World in the Balance: In Double Up, calculate how long it takes a country s population to double in size and investigate factors affecting growth rate.

3. Globally, there was no improvement in physical activity from 2001 to 2016. In fact, high-income Western countries got worse -- from 31 percent inactive in 2001 to 37 percent in 2016.

Globally, 27.5% of adults do not get enough exercise, according to the World Health Organization. High-income countries are most inactive. It's a global problem that needs to be 'urgently addressed' ...

Classroom Activity for the NOVA program World in the Balance: ... For example, if a town had 75 people in 1980 and 100 people in 1981, the growth rate for the year would be 33 percent.