Question

Answer 1

Bài 1:
a. 

$\frac{2}{5}+\frac{3}{5}=\frac{2+3}{5}=\frac{5}{5}=1$

b.

$\frac{7}{4}-\frac{3}{5}=\frac{7.5-3.4}{4.5}=\frac{23}{20}$

c.

$\frac{2}{3}.\frac{1}{2021}+\frac{2022}{2021}.\frac{2}{3}-\frac{2}{3}$

$=\frac{2}{3}(\frac{1}{2021}+\frac{2022}{2021}-1)$

$=\frac{2}{3}(\frac{1}{2021}+\frac{1}{2021}+1-1)$

$=\frac{2}{3}.\frac{2}{2021}=\frac{4}{6063}$

Answer 2

Bài 2:

a. 
$x+9,25=17,75$

$x=17,75-9,25=8,5$

b.

$\frac{2}{3}x-\frac{5}{7}=\frac{9}{7}$

$\frac{2}{3}x=\frac{9}{7}+\frac{5}{7}=\frac{14}{7}=2$
$x=2: \frac{2}{3}=3$