easily deceived, tricked, or fooled
Illiterate people tend to be gullible because their knowledge of the world is so limited that they often do not know when they are being lied to.
Gullible = Gull + ible = girl/galli + able A girl who is able to be tricked or deceived easily. gali = street (in hindi). street people like slum can be easily deceived (although the other way is also true)