If the price of ordinary tickets is X (yuan/piece), the price of group tickets is X (1-20%) = 0.8x (yuan/piece).

120x- 120×0.8x=2880

120x-96x=2880

24x=2880

x= 120

That is, the price of ordinary tickets is 120 (yuan/piece), and the price of group tickets is 0.8× 120=96 (yuan/piece).