Mary, Peter, and Lucy were picking chestnuts. Mary picked twice as many chestnuts than Peter. Lucy picked 2 kg more than Peter. Together the three of them picked 26 kg of chestnuts. How many kilograms did each of them pick?

Let x be the amount Peter picked. Then Mary and Lucy picked 2x and x+2, respectively. So

x+2x+x+2=26

4x=24

x=6

Therefore, Peter, Mary, and Lucy picked 6, 12, and 8 kg, respectively.