I'll answer with an image.

A somewhat higher percentage of Negroes (14 per cent) believe police brutality exists in their area than is true among whites (6 per cent)

I'd say the number of "Negroes" believing that police brutality exists in their area would be more closer to 90%... these are the 1960s we're talking about.

Nearly a third (27%)

27% is closer to a quarter than a third.