Then y 1=0.8x, y2=x(x is less than or equal to 200), 200+0.7(x-200)(x is greater than 200).
When y 1=y2, the solution is x=600 (yuan).
When y 1 is greater than y2, the solution is that x is greater than 600 yuan.
When y 1 is less than y2, x is less than 600 yuan.
As can be seen from the above, when the consumption amount is 600 yuan, shopping malls A and B are the same: when the consumption amount is greater than 600 yuan, it is more economical to go to shopping malls B; When spending is within 600 yuan, it's cheaper to go to Mall A..