A retail store sells two types of walnuts, the Indian walnuts at 120/kilo and chestnuts at $ 60/kilo. How many pounds of each type should Rogelio buy to have a mixture of 20 kilos sold at 80/kilo?

To solve this problem, we first need to find out the overall ratio of Indian walnuts to chestnuts to give an average price of $80 / Kilo. We know that Indian walnuts are sold at $120 / Kilo and the chestnuts are sold at $60 / Kilo. The difference between the two prices is $60. Next, to get an average of $80, we find out how far each nut is away from the average. Chestnuts are $20 away and Indian walnuts are $40. Dividing this by the difference of $60 gives you 1/3 for the chestnuts and 2/3 for the walnuts. Finally, you multiply each fraction by 20 pounds to give you how many pounds of each you need to buy to give you an average cost of $80 / Kilo. So for the Indian walnuts, you get 20 X 2/3 = 13 1/3 Kilos. And for the chestnuts, you get, 20 X 1/3 = 6 2/3 Kilos. So, Rogerio would need to buy 13 1/3 Kilos of Indian walnuts and 6 2/3 Kilos of chestnuts to give him an average cost of $80 / Kilo.