Giải Bài 11 trang 13 sách bài tập toán 7 tập 1 - Cánh diều

Đề bài

Tính:

a) $- {\rm{ }}6,07 + 3,68$;                                            

b) $\dfrac{3}{5} + ( - {\rm{ }}4)$;

c) $1\dfrac{3}{5} - \dfrac{{ - 7}}{{11}}$;                                    

d) $\dfrac{{ - 7}}{{13}} + 0,6$;

e) $- {\rm{ 1,221}}{\rm{.}}\dfrac{2}{{ - 5}}$;                           

g) $\dfrac{{ - 17}}{7}:0,25$.

Lời giải chi tiết

a) $- {\rm{ }}6,07 + 3,68 =-(6,07-3,68)=  - {\rm{ 2,39}}$;                              

b) Do $\dfrac{3}{5} = \dfrac{6}{{10}} = 0,6$ nên:

$\dfrac{3}{5} + ( - {\rm{ }}4) = \dfrac{3}{5} - 4 = 0,6 - 4 =-(4-0,6)=  - 3,4$;

c) $1\dfrac{3}{5} - \dfrac{{ - 7}}{{11}} = \dfrac{8}{5} + \dfrac{7}{{11}} = \dfrac{{88}}{{55}} + \dfrac{{35}}{{55}} = \dfrac{{123}}{{55}}$;                                

d) $\dfrac{{ - 7}}{{13}} + 0,6 = \dfrac{{ - 7}}{{13}} + \dfrac{6}{{10}} = \dfrac{{ - 70}}{{130}} + \dfrac{{78}}{{130}} = \dfrac{8}{{130}} = \dfrac{4}{{65}}$;

e) Do $\dfrac{2}{{ - 5}} = \dfrac{4}{{ - 10}} =- 0,4$ nên:

 $- {\rm{ 1,221}}{\rm{.}}\dfrac{2}{{ - 5}} =  (- {\rm{ 1,221}}){\rm{.}}( - {\rm{ 0,4) = 0,4844}}$;       

g) $\dfrac{{ - 17}}{7}:0,25 = \dfrac{{ - 17}}{7}:\dfrac{1}{4} = \dfrac{{ - 17}}{7}.4 = \dfrac{{ - 68}}{7}$.