A shopkeeper gives one kite free to a customer on purchase of 19 kites. If he doubles the discount, how many kites should he give free on purchase of 27 kites?

3

No. of kites free = 1

No. of kites sold = 19 + 1 = 20

Sale = 20 kites (constant)

ATQ, shopkeeper did not increase sale but double the discount only.

It means no. of articles sale will be 20 kites but he gives 2 kites free instead of 1.

Therefore, 

on selling 20 kites, free kites = 2

on selling 10 kites, free kites = 1

on selling 30 kites, free kites = 3

Hence, on purchase of 27 kites, 3 kites will be free.