Iam trying to solve a question from genetic epidemiology.
but my math knowledge is pathetic.
Could you please verify the steps and the solution ?

question: Given p(B)= .25,p(AB)=.5,p(A)=.4, what is the standardised gametic disequilibirium coefficient D'?
(where B,A represents alleles)
looking at the lecture slides i find:
D'={delta/delta Max for delta >= 0
D'={delta/-delta Min for delta =< 0

delta max is given as min(-p(A).p(b), -p(a).p(B))

for haplotype AB,
(gametic disequilibirium coefficient) delta =P(AB)-P(A).p(B)
delta =.5-.1=.4


delta max= min(-.4*.25,- .6*.75)= min(-.1,-.45)=-.45

finally D'=.4/-.45=-.889

Please feel free to correct ridiculous mistakes i must have made..thanks