1, Tính bằng cách thuận tiện
a,(6/9+1/3).3/4+1/4.(17/221+12/13)
b, 2 và3/4+5 và2/3-0,75-4 và1/3
b,20202020.2019-20192019.2020
3 ,Tìm x
a,2/5.(x- 1/2)=800
b, 10,25 :(2020-x)=0,125
c, x:2+x:3+x4=13
d, x:1/2=x+1/3
(Lưu ý . Có nghĩa là nhân)
Giúp em vs mọi người
1) a) ($\frac{6}{9}$+$\frac{1}{3}$)×$\frac{3}{4}$+$\frac{1}{4}$×($\frac{17}{221}$+$\frac{12}{13}$)
=($\frac{2}{3}$+$\frac{1}{3}$)×$\frac{3}{4}$+$\frac{1}{4}$×($\frac{1}{13}$+$\frac{12}{13}$)
=1.$\frac{3}{4}$+$\frac{1}{4}$.1
=$\frac{3}{4}$+$\frac{1}{4}$=1
b) $2\frac{3}{4}$+$5\frac{2}{3}$-0,75-$4\frac{1}{3}$
=(2+$\frac{3}{4}$)+(5+$\frac{2}{3}$)-0,75-(4+$\frac{1}{3}$)
=2+0,75+5+$\frac{2}{3}$-0,75-4-$\frac{1}{3}$
=3+$\frac{1}{3}$=$3\frac{1}{3}$=$\frac{10}{3}$
c) 20202020×2019-20192019×2020
=2020×10001×2019-2019×10001×2020
=0
2) a) $\frac{2}{5}$×(x-$\frac{1}{2}$)=800
⇒ x-$\frac{1}{2}$=800÷$\frac{2}{5}$=2000
⇒ x=2000+$\frac{1}{2}$=$2000\frac{1}{2}$
b) 10,25÷(2020-x)=0,125
⇒ 2020-x=10,25÷0,125=82
⇒ x=2020-82=1918
c) x÷$\frac{1}{2}$=x+$\frac{1}{3}$
⇒ 2×x=x+$\frac{1}{3}$
⇒ 2×x-x=$\frac{1}{3}$
⇒ x=$\frac{1}{3}$