(1) class b: 70×2= 140 yuan.
So 189- 140=49 yuan.
(2) Buy X for the first time and 70-x for the second time.
It is discussed in three situations.
( 1) x < 20,70 x > 50。
Then 3x+2(70-x)= 189.
The solution is x=49 (it does not meet the range of x value, so it is discarded).
② 20 < x < 30 and 40 < 70-x < 50.
The equation is 3x+2.5(70-x)= 189.
The solution is x = 28- consistent! ! !
③ 30 < x < 35 (because the second time is greater than the first time), then 35 < 70-x < 40.
The equation is 2.5x+2.5(70-x)= 189.
X has no solution
To sum it up. There is x=28,
Answer: I bought 28 kg for the first time and 42 kg for the second time!
Is that clear ~ ~:) Here you are ~ ~ Hehe.