(1) * * The total amount is198/0.9+500/0.9+54/0.8 = 843.06 yuan.

If discount is used, it will be 500*0.9+343.06*0.8=724.45 yuan.

So a one-time purchase is only 724.45 yuan.

(2) The product with a price of 750 should be 500*0.9+250*0.8=650 yuan.

Goods from 750 yuan can only be bought in 650 yuan.