1/
a) $\frac{-5}{2}$ : ($\frac{3}{4}$ - $\frac{1}{2}$)
= $\frac{-5}{2}$ : ($\frac{3}{4}$ - $\frac{2}{4}$)
= $\frac{-5}{2}$ : $\frac{1}{4}$
= $\frac{-5}{2}$ . $\frac{4}{1}$
= -10.
b) $\frac{298}{719}$ : ($\frac{1}{4}$ + $\frac{1}{12}$ - $\frac{1}{3}$) - $\frac{2011}{2012}$
= $\frac{298}{719}$ : ($\frac{3}{12}$ + $\frac{1}{12}$ - $\frac{4}{12}$) - $\frac{2011}{2012}$
= $\frac{298}{719}$ : 0 - $\frac{2011}{2012}$
= 0 - $\frac{2011}{2012}$
= $\frac{-2011}{2012}$.
c) $\frac{27.18 + 27.103 - 120}{15.33 + 33.12}$
= $\frac{27 . (18 + 103) - 120}{33 . (15 + 12)}$
= $\frac{27 . 121 - 120}{33.27}$
= $\frac{121 - 120}{33}$
= $\frac{1}{33}$.
2/
a) (x - $\frac{5}{8}$) . $\frac{5}{18}$ = $\frac{-15}{36}$
x - $\frac{5}{8}$ = $\frac{-15}{36}$ : $\frac{5}{18}$
x - $\frac{5}{8}$ = $\frac{-15}{36}$ . $\frac{18}{5}$
x - $\frac{5}{8}$ = $\frac{-3}{2}$
x = $\frac{-3}{2}$ + $\frac{5}{8}$
x = $\frac{-12}{8}$ + $\frac{5}{8}$
x = $\frac{-7}{8}$.
b) |x - $\frac{1}{5}$| = $\frac{5}{6}$
=> x - $\frac{1}{5}$ = $\frac{5}{6}$ hoặc $\frac{-5}{6}$
TH1 : x - $\frac{1}{5}$ = $\frac{5}{6}$
x = $\frac{5}{6}$ + $\frac{1}{5}$
x = $\frac{25}{30}$ + $\frac{6}{30}$
x = $\frac{31}{30}$.
TH2 : x - $\frac{1}{5}$ = $\frac{-5}{6}$
x = $\frac{-5}{6}$ + $\frac{1}{5}$
x = $\frac{-25}{30}$ + $\frac{6}{30}$
x = $\frac{-19}{30}$.
Vậy x = $\frac{31}{30}$ hoặc $\frac{-19}{30}$.
3/ Giải
`2/7` chiều rộng là :
70 x 40% = 28 (m)
Chiều rông mảnh đất là :
28 : `2/7` = 98 (m)
Chu vi mảnh đất là :
(98 + 28) x 2 = 252 (m)
Diện tích mảnh đất là :
98 x 28 = 2744 ($m^{2}$)
