a,-2/7 + 2/7 : 3/5.          b,-8/19 + -4/21 - 17/21 + 27/19

=-2/7 + (2/7 : 3/5)         =(-4/21 + 17/21) + (-8/19 + 27/19)

=-2/7 + 10/21.                =-1 + 1                                   

=16/21.                            =0

c, 6/5 . 3/13 - 6/5 . 16/13

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

=6/5 . -1 

=-6/5

chiều rộng của Một đám đất là:

60:30 =2(m)

diện tích của Một đám đất là:

4/3.2=8/3

diện tích ao thả cá là:

7/12+8/3=31/4(m)

đáp số: 31/4 m

M={4/5;5/6;6/5;...}

M={4/5;5/6;6/5;...}

1, ABF;ACD;DEB;CEF;FEC;DCA;FBA.

2. 

a, 9-4=5(cm)

b, 8-2=6(cm)

    6+4+10(cm)

Đáp số: a,5cm

               B,10cm

a,-5/9 + 8/15 + -2/11 + 4/-9 + 7/15               b,(7/2 . 5/6) + (7/6 : 2/7)

=(-5/9 + -4/9) + (8/15 + 7/15) + -2/11           =35/12 + 49/12

=-1 + 1 + -2/11                                                   =84/12

=0 + -2/11                                                           =42/6

=-2/11                                                                  =21/3

                                                                               =7

a,-5/9 + 8/15 + -2/11 + 4/-9 + 7/15               b,(7/2 . 5/6) + (7/6 : 2/7)

=(-5/9 + -4/9) + (8/15 + 7/15) + -2/11           =35/12 + 49/12

=-1 + 1 + -2/11                                                   =84/12

=0 + -2/11                                                           =42/6

=-2/11                                                                  =21/3

                                                                               =7

a,-3/8 < 5/-12

b,3131/5252 = 31/52

a,-3/8 > 5/-12

b,3131/5252 = 31/52