Black fur (b) in guinea pigs is dominant over white fur (b). find the probability of a hybrid offspring in the cross: bb x bb. 0% 25% 50% 75% 100%

If you were referring to a cross between BB and Bb genotype then the answer would be 50%.

You can figure this out by making a Punnett Square.

B b

B BB Bb

B BB Bb

If you look at the result there is a chance that 2 out of the 4 will have a mixed genotype of Bb. The probability would then be 50%.