basic skill

I. 1，D 2，D 3，D 4，c。

2, 5, 275 6, 250 7, 175, 250, 500 1, 1 175.

3.8. Let's assume that the cost price of each of these jackets is X yuan.

X( 1+0.5)*0.8=60

X=50

9. Let the original price be X yuan.

x * 0.8( 1-0. 1)= 144

X=200 (yuan)

Expansion and improvement

I. 1，A 2，B

2, 3, 1.5 4, ( 1)3, 3, 5.8; 3,3,6 (2)②

3，5，( 1)39，22，858 (2)38，24，9 12 (3)(40-X)，(20+2X)，(40-X)*(20+2X)，(4)

6、0.6X+20=0.8X- 15

X= 175