Câu 1:
a) $\frac{3}{11}$ + $\frac{-7}{11}$ + $\frac{13}{11}$
= $\frac{-4}{11}$ + $\frac{13}{11}$
= $\frac{9}{11}$
b) $\frac{2}{7}$ x $\frac{21}{4}$ x $\frac{9}{5}$
= $\frac{3}{2}$ x $\frac{9}{5}$
= $\frac{27}{10}$
c) $\frac{6}{13}$ : $\frac{5}{26}$
= $\frac{6}{13}$ x $\frac{26}{5}$
= $\frac{12}{5}$
d) $\frac{1}{2}$ + $\frac{3}{4}$ : ($\frac{-6}{7}$)
= -0,825 + 0,5
= -0,375
e) $\frac{7}{19}$ x $\frac{8}{11}$ + $\frac{7}{19}$ x $\frac{3}{11}$ + $\frac{12}{19}$
= $\frac{7}{19}$ x ($\frac{8}{11}$ + $\frac{3}{11}$) + $\frac{12}{19}$
= $\frac{7}{19}$ x 1 + $\frac{12}{19}$
= $\frac{7}{19}$ + $\frac{12}{19}$
=1
f) $\frac{-7}{21}$ + (1-$\frac{1}{3}$)
= $\frac{-7}{21}$ + $\frac{2}{3}$
=$\frac{1}{3}$
Câu 2:
chiều rộng mảnh vườn là:
7,2 x 60 : 100 = 4,32 (m)
chu vi mảnh vườn là:
(4,32 + 7,2) x 2 = 23,04 (m)
diện tích mảnh vườn là:
4,32 x 7,2 = 31,104 (m²)
đáp số: chu vi: 23,04 m
diện tích: 31,104 m²
Câu 3:
a) x + $\frac{5}{3}$ = $\frac{1}{81}$
x = $\frac{1}{81}$ - $\frac{5}{3}$
x = $\frac{-1}{81}$
b) $\frac{3}{4}$ : x - $\frac{-1}{2}$ = $\frac{1}{10}$
$\frac{3}{4}$ : x = $\frac{1}{10}$ + $\frac{-1}{2}$
$\frac{3}{4}$ : x = $\frac{-2}{5}$
x = $\frac{3}{4}$ : $\frac{-2}{5}$
x = -1,875
c) $\frac{3}{5}$.x=$\frac{3}{7}$
x = $\frac{3}{7}$ : $\frac{3}{5}$
x = $\frac{5}{7}$
d) $\frac{5}{2}$ : x = $\frac{-4}{25}$
x = $\frac{5}{2}$ : $\frac{-4}{25}$
x= -15,623
