In a class of 39 where girls are twice to that of boys.  Shalini, a girl 10th from the top. If there are 5 girls ahead of her then, how many boys are after her? 

9

 Number of girls are twice to that of boys. 

i.e.   G = 2B 

Total number of students = 39 

 G + B = 39

 2B + B = 39 

 3B = 39 

B= 13 ( number of boys) 

 G= 26 ( number of girls ) 

Now, 

Shalini is 10th from top and 5 girls are ahead of her . That means there are are 4 boys ahead of her . 

So, number of boys after shalini = total number of boys - number of boys ahead of her 

                                               = 13 - 4 = 9