Read The Bell Curve (Murray & Herrnstein). It's well worth reading since it covers the importance of IQ for all kinds of outcomes in addition to describing IQ averages by race. It's a bit dated but the data and conclusions are just as true today.
In short, the average Black IQ is about one standard deviation below the average for Whites. There's a lot of variance within each group so you have dumb Whites and smart Blacks, but on average there is a substantial difference. This basically accounts for almost all differences in outcomes (income, marriage rates, birth rates, welfare reliance, crime rates, etc.) between the races.
Bell Curve is a great book, redpills you about class as well.
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