How did desertification affect early human civilizations in northern africa

Well, back in the 19th century people had to grow food in order to eat. With the land being a dry and open land of desert and if you didn't know desert land is dry, plants need moist and humid lands to grow. The people of Africa are effected by this because it makes the incapable to produce crops. Even today land in Africa makes them unable to produce crops but in today's society there are shops and transported goods to Africa.

Explanation:

answer: wait what

explanation:

part a. there were 250 teenagers surveyed (100% of tenagers = 250)therefore 1 % = 250/100 = 2.5 76% = 1% x 76 = 2.5 x 76 = 190 teenagers of the 250 surveyed liked burgerspart b: jane surveyed 25% (which is equal to 50 teenagers, i.e. a quarter of the teenagers surveyed is 50) to get 100% we simply get 4 quarters, i.e. multiply 50 by 4 = 200 teenagers were surveyed by jane. part c: it is impossible to give an example where a percentage is greater than 100%, since, by definition , percentage means "per 100".