(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