Bài `7 :`

`a, Đ`

`b, S`

`c, S`

`d, Đ`

Bài `8 :`

`a,3 1/5 + 2 1/2 = 16/5 + 5/2 = 32/10 + 25/10 = 57/10`

`b, 4 2/3 - 2 1/2 = 14/3 - 5/2 = 28/6 - 15/6 = 13/6`

`c, 5 1/4 xx 2 2/3 = 21/4 xx 8/3 = 14`

`d, 3 5/6 : 2 3/4 = 23/6 : 11/4 = 23/6 xx 4/11 = 46/33`

Bài `9 :`

`1 1/15 xx 1 1/16 xx 1 1/17 xx ..... x 1 1/2009 xx 1 1/2010`

`= 16/15 xx 17/16 xx 18/17 xx .... xx 2010/2009 xx 2011/2010`

`= ( 16 xx 17 xx 18 xx .... xx 2010 xx 2011 )/( 15 xx 16 xx 17 xx .... xx 2009 xx 2010 )`

`= 2011/15`

Bài `10 :`

`471/709 xx 49/57 + 471/709 xx 8/57`

`= 471/709 xx ( 49/57 + 8/57 )`

`= 471/709 xx 1`

`= 471/709`

Đáp án+Giải thích các bước giải:

7.

`a) 3 7/(10)= (3 xx 10+7)/(10)=(37)/(10) ->Đ`

`b) 4 2/3= (4 xx 3+2)/3=(14)/3 ->S`

`c) 12 5/8=(12 xx 8 +5)/8=(101)/8 ->S`

`d) 13 1/4=(13 xx 4+1)/4=(53)/4 ->Đ`

8.

`a) 3 1/5+2 1/2`

`= (3 xx5+1)/5+(2xx2+1)/2`

`=  (16)/5+ 5/2`

`=(32)/(10)+(25)/(10)`

`=(57)/(10)`

`b) 4 2/3-2 1/2`

`=(4xx3+2)/3-(2xx2+1)/2`

`= (14)/3-5/2`

`=(28)/6-(15)/6`

`= (13)/6`

`c) 5 1/5 xx 2 2/3`

`= (5xx5+1)/5 xx (2xx3+2)/3`

`= (26)/5 xx 8/3`

`=(208)/(15)`

`d) 3 5/6 : 2 3/4`

`=(3xx6+5)/6:(2xx4+3)/4`

`=(23)/6:(11)/4`

`=(23)/6 . 4/(11)`

`= (46)/(33)`

9.

`1 1/(15) xx 1 1/(16)xx 1 1/(17)xx...xx1 1/(2009)xx 1 1/(2010)`

`=(1+1/(15))xx(1+1/(16))xx(1+1/(17))xx...xx(1+1/(2009))xx(1+1/(2010))`

 `=(16)/(15)xx(17)/(16)xx(18)/(17)xx...xx(2010)/(2009)xx(2011)/(2010)`

`=(2011)/(15)`

10.

`(471)/(709)xx(49)/(57)+(471)/(709)xx8/(57)`

`=(471)/(709)xx((49)/(57)+8/(57))`

`=(471)/(709)xx(57)/(57)`

`=(471)/(709)xx1`

`=(471)/(709)`