Giải thích các bước giải:
Bài 1:
a, (13$\frac{3}{7}$ + 4$\frac{5}{13}$) - 8$\frac{3}{7}$
= 13$\frac{3}{7}$ + 4$\frac{5}{13}$ - 8$\frac{3}{7}$
= 13$\frac{3}{7}$ - 8$\frac{3}{7}$ + 4$\frac{5}{13}$
= 5+ + 4$\frac{5}{13}$ = + 9$\frac{5}{13}$
b, (6- 2$\frac{4}{5}$)3$\frac{1}{8}$ - 1$\frac{3}{5}$ : $\frac{1}{4}$
= ($\frac{30}{5}$ - $\frac{14}{5}$)$\frac{25}{8}$ - $\frac{8}{5}$.$\frac{4}{1}$
= $\frac{16}{5}$.$\frac{25}{8}$ - $\frac{8}{5}$.$\frac{4}{1}$
= 10-$\frac{32}{5}$ = $\frac{18}{5}$
c, $\frac{-2}{3}$.$\frac{5}{8}$+$\frac{5}{8}$.$\frac{3}{5}$
= $\frac{5}{8}$.($\frac{-2}{3}$+$\frac{3}{5}$)
= $\frac{5}{8}$.$\frac{-1}{15}$ = $\frac{-1}{24}$
d, 25% - 1$\frac{1}{2}$ + 0,5.$\frac{12}{5}$
= $\frac{1}{4}$-$\frac{3}{2}$ + $\frac{1}{2}$.$\frac{12}{5}$
= $\frac{1}{4}$-$\frac{3}{2}$ + $\frac{6}{5}$
= $\frac{5}{20}$-$\frac{30}{20}$ + $\frac{24}{20}$
= $\frac{-1}{20}$
e, 0,25.2$\frac{1}{3}$.30.0,5.$\frac{8}{45}$
= $\frac{1}{4}$.$\frac{7}{3}$.$\frac{30}{1}$.$\frac{1}{2}$.$\frac{8}{45}$
= $\frac{1.7.30.1.8}{4.3.1.2.45}$
= $\frac{14}{9}$
Bài 2:
a, (4,5 - 2x).1$\frac{4}{7}$ = $\frac{11}{14}$
(4,5 - 2x).$\frac{11}{7}$ = $\frac{11}{14}$
$\frac{9}{2}$ - 2x = $\frac{11}{14}$.$\frac{7}{11}$
$\frac{9}{2}$ - 2x = $\frac{1}{2}$
2x = $\frac{9}{2}$ - $\frac{1}{2}$
2x = 4
x = 4 : 2
x = 2
Vậy x = 2
b, (2,8x - 32) : $\frac{2}{3}$ = -90
(2,8x - 32) : $\frac{2}{3}$ = $\frac{-90}{1}$
($\frac{14}{5}$x - 32) : $\frac{2}{3}$ = $\frac{-90}{1}$
$\frac{14}{5}$x - 32 = $\frac{-90}{1}$.$\frac{2}{3}$
$\frac{14}{5}$x - 32 = -60
$\frac{14}{5}$x = -60 + 32
$\frac{14}{5}$x = -28
x = $\frac{-28}{1}$:$\frac{14}{5}$
x=-10
Vậy x =-10
c, 8x = 7,8x + 25
8x = $\frac{39}{5}$ + 25
8x - $\frac{39}{5}$ = 25
$\frac{1}{5}$x = 25
x = 25 : $\frac{1}{5}$
x= 125
Vậy x = 125
d, $\frac{3}{x+5}$ = 15%
$\frac{3}{x+5}$ = $\frac{3}{20}$
(x+5).3= 3.20
3x + 15 = 60
3x = 60 - 15
3x = 45
x = 45 : 3
x = 15
Vậy x = 15
