Solution: Assume that the adult ticket is X yuan and the child ticket is 0.5X yuan.

2X+0.5X=22.5

2.5 times =22.5

X=22.5÷2.5

x=9

A: One adult ticket, 9 yuan.

(1)38.7x2=77.4 yuan

(2) 38.7x0,7x3 = 81.27 yuan.

77.4 yuan < 8 1.27 yuan

Star bakery is cheaper.