3. Amit donated 20% of his income to a school and deposited 20% of the remainder in his bank. If he is having Rs 12800 now, then what is the income (in Rs) of Amit?
4. A trader sold an article at profit of 20%. Had he bought that article at 60% less price and sold it at Rs 90 less, then he would have gained 50%. What is the value (in Rs) of cost price?
5. A dishonest shopkeeper professes to sell his groceries at his cost price but uses a false weight of 900 grams for each kilogram. Find his gain percentage.