a M la trung diem cua AB nen

AM=MB=AB/2=4/2=2cm

b

vi A,M,B thang hang nen

AMB=180 do

goc can tim

xMy=180 do-50 do-70 do=60 do

xMy=60 do

so hoc sinh trung binh la

40.1/8=5

so hoc sinh kha la

14+5=19

so hoc sinh gioi la

40.7/20=14

so ho sinh yeu la

40-(14+5+19)=2

1a

-14/3

1b

0

1c

9/5

2/1.3=1/1-1/3

2/3.5=1/3-1/5

2/5.7=1/5-1/7

.....

2/99.101=1/99-1/101

(1-1/3)+(1/3-1/5)+(1/5-1/7)+.....+(1/99-1/101)

1-1/101=100/101

ket qua 100/101

1a thuoc BD:B,C.D

khong thuoc BD:A,E

1b

AB song song voi DE

1c

AE cat BD tai C

AB cat AE tai A

AB cat BD tai B

DE cat BD tai D

DE cat AE tai E

2

AB=6-4=2cm

AM=MB=1cm

OM=4+2=5cm

vay chieu dai OM la 5cm

quy dong;

2/9=6/27

1/3=3/27

5/27=5/27

so sanh

9/27>6/27>5/27 hay 1/3>2/9>5/27

nen

doi 2 lam nhieu nhat

doi 3 lam it nhat

b giai

so phan cong viec ca 3 doi lam chung 1h la:

6/27+9/27+5/27=20/27

trong 1h ca 3 doi lam duoc 20/27 phan cong viec

a x-2/3=-5/12

x=-5/12+2/3

x=-5/12+8/12

x=3/12=1/4

vay x= 1/4

b 8/5:x=-2/3

x=8/5:-2/3

x=8/5.-3/2

x=4/5.-3/1

x=-12/5

vay x = -12/5

c 1-3/7.x=-2/7

3/7.x=1--2/7

3/7.x=7/7+2/7

3/7.x=9/7

x=9/7:3/7

x=9/7.7/3

x=3/1.1/1

x=3

vay x =3

a -2/7+2/7:3/5

=(-2/7+2/7):3/5

=0:3/5

=0.5/3

0

b -8/19+-4/21-17/21+27/19

=(-8/19+27/19)+(-4/21-27/19)

=1+-1

=0

c 6/5.3/13-16/13.6/5

=6/5.(3/13-16/13)

=6/5.-1

=-6/5