What are those numbers? I'm assuming they are the racial distribution of new AIDS cases over some recent period.
The % of new AIDS cases from a group isn't as important to this analysis as the % of the group that has AIDS.
For example, we have 1,000,000 people. For simplicity, we'll say that each person is either White or Black, Male or Female, Homosexual or Heterosexual. I'm making up these numbers to show a concept, so don't get too hung up on them.
Code:
[FONT=Arial][FONT=Trebuchet MS][SIZE=2]White 60% Male 55% Hetero 95%[/SIZE][/FONT]
[SIZE=2][FONT=Arial]Black 40% Female 45% Homo 5%[/FONT][/SIZE]
[SIZE=2][FONT=Arial] # of people % with AIDS # with AIDS [/FONT][/SIZE]
[SIZE=2][FONT=Arial]White Male Hetero 313,500 0.05% 156.75 [/FONT][/SIZE]
[SIZE=2][FONT=Arial]White Male Homo 16,500 4.00% 660.00 [/FONT][/SIZE]
[SIZE=2][FONT=Arial]White Female Hetero 256,500 0.05% 128.25 [/FONT][/SIZE]
[SIZE=2][FONT=Arial]White Female Homo 13,500 0.01% 1.35 [/FONT][/SIZE]
[SIZE=2][FONT=Arial]Black Male Hetero 209,000 0.05% 104.50 [/FONT][/SIZE]
[SIZE=2][FONT=Arial]Black Male Homo 11,000 7.00% 770.00 [/FONT][/SIZE]
[SIZE=2][FONT=Arial]Black Female Hetero 171,000 0.10% 171.00 [/FONT][/SIZE]
[SIZE=2][FONT=Arial]Black Female Homo 9,000 0.05% 4.50 [/FONT][/SIZE][/FONT]
A couple of things to note:
The overall AIDS rate of the population is 0.20%
Blacks make up 52.6% of the people who have AIDS, but 73% of the black AIDS cases are coming from black homosexual males, who make up only ~3% of the black population. Out of all blacks, 0.26% of them have AIDS.
If we remove homosexual males from the equation, then blacks still make up ~50% of the AIDS cases, but it is 50% of a much smaller number. Non-"homosexual male"-blacks have a 0.07% AIDS rate. We have removed ~3% of the population.
If we remove blacks from the equation then the overall rate of AIDS in the remaining population will be 0.16%. We have removed 40% of the population.
If we remove blacks and white-homosexual-males from the population the rate of AIDS in the remainder is 0.05%
So, eliminating homosexual men drops the overall AIDS rate from 0.2% to 0.07%. Eliminating blacks only drops the overall AIDS rate from 0.2% to 0.16%. Eliminating Blacks and homosexual men takes us to 0.05% (blacks only bought us 0.02% on top of the homosexual males).
In this example, the "homosexual male"-ness captures the HIV cases much better than the "black"-ness does, and it does so by removing only ~3% of the population.
Again, the whole point here is that the 51% that you quote is fairly worthless in this discussion.