If a person's income increases from Rs 20 lakhs per year to Rs 24 lakhs per year and tax increases from Rs 3,50,000 to Rs 4,00,000 the marginal tax rate is
A man has some hens and some cows. If the total number of heads of hens and cows together is 50 and the nunber of feet of hens and cows together is 142, then the number of cows is