The number of geometrical isomers optical possible for the compound with the structure ${\mathrm{CH}}_3\mathrm{CH}=\mathrm{CH}–\mathrm{CH}=\mathrm{CH}–{\mathrm{CH}}_2{\mathrm{CHOHCH}}_3$ is

The number of geometrical isomers optical possible for the compound with the structure ${\mathrm{CH}}_3\mathrm{CH}=\mathrm{CH}–\mathrm{CH}=\mathrm{CH}–{\mathrm{CH}}_2{\mathrm{CHOHCH}}_3$. 

step 1:- find the carbon-carbon (double) bonds
step 2:- find the chiral carbon 
step 3:- form different sets of cis and trans of all the sets of carbons 
step 4:- no of isomers is $2^{\mathrm{n}}$ (n=no of double-bonded carbon sets)

In this case n=3, thus the number of isomers is 8.