(2) Assume that the price of the purchased goods is X yuan.

Scheme 1: 168+0.8X shall be paid.

Option 2, should pay 0.95X yuan.

If the first scheme is more economical, then168+0.8x < 0.95x.

0. 15X> 168

X> 168÷0. 15

X> 1 120

That is, when the price of purchased goods is greater than 1 120 yuan, the first scheme is more cost-effective.

Two. Why are there black balls?

Three. Solution: 2 minutes is 120 seconds.

Suppose it is 30 seconds x times, it will take 30x seconds.

So 15 seconds and 120-30x seconds.

Can be played (120-30x)/15 =120/15-30x/15 = 8-2x times.

At least 2 times

So x> = 2,8-2x > =2

2x & lt=6

x & lt=3

So x=2 or 3.

So there are two kinds.

Four. Can refer to it