From the article:<p>>40 per cent of the world's 8.2 billion people live in rural areas<p>>the rural population is underestimated by half<p>Based on the first statement:
8.2*0.4=3.28 billion rural globally;<p>And according to the second statement, there re actually twice as many, so another 3.28 billion people, or:<p>8.2+3.28=over 11 billion in total on Earth.