In a class of 60, where girls are twice that of boys, Amal ranked seventeenth from the top. If there are 9 girls ahead of Amal, how many boys are after him in rank ?

Given that in a class there 60 students.

Given girls are twice that of boys, it means $G:B=2:1$

Hence, the number of girls is 40 and the number of boys is 20. 

Amal ranked 17 from top, 

Given that 9 girls are ahead of amal, so that 7 boys are ahead

Remaining boys are $\left(20-7-1\right)=12$ boys are after him in rank

Therefore, the required number is $\boxed{12}$