The marked price of a shirt and trousers are in the ratio 1:2. The shopkeeper gives 40% discount on the shirt. If the total discount in the set of the shirt and trousers is 30%, the discount offered on the trousers is:

Let the price of shirt and trouser be Rs. 100 and Rs. 200 respectively.
Then, price of set of shirt and trouser = Rs. 300.
After giving 30% discount on the set,
Selling Price = 300 - 30% of 300 = 210.
Total Discount on Set = 90.
And Discount on shirt is 20% alone,
SP of shirt alone = 100 - 40% of 100 = 60.
Rs. 40 is the discount on shirt then Rs. 50 must be the discount on the trouser.
So, discount on trouser = $$\frac{{50 \times 100}}{{200}}$$  = 25%.