1, \(\frac{5}{21}+0,5-\frac{19}{23}+\frac{16}{21}-\frac{4}{23}\)

\(=\frac{5+16}{21}-\frac{19+4}{23}+0,5\)

\(=1-1+0,5\)

\(=0,5\)

2,\(\frac{27}{23}+\frac{5}{21}-\frac{4}{23}+\frac{6}{21}+\frac{1}{2}\)

\(=\frac{27-4}{23}+\frac{5+6}{21}+\frac{1}{2}\)

\(=1+\frac{11}{21}+\frac{1}{2}\)

\(=\frac{42+22+21}{42}\)

\(=\frac{85}{42}\)

\(\frac{28}{23}+\frac{19}{21}-\frac{5}{23}+\frac{7}{10}+\frac{2}{21}\)

\(=\left(\frac{28}{23}-\frac{5}{23}\right)+\left(\frac{19}{21}+\frac{2}{21}\right)+\frac{7}{10}\)

\(=\frac{23}{23}+\frac{21}{21}+\frac{7}{10}\)

\(=1+1+\frac{7}{10}=2\frac{7}{10}=2,7\)

28/23+19/21-5/23+7/10+2/21 = 2,7 nhé

28/23+19/21-5/23+7/10+2/21=(28/23-5/23)+(19/21+2/21)+7/10=23/23+21/21+7/10=1+1+7/10=2+7/10=27/10

S1 = 1 + 2 + 3 + 4 + ... + 999

= (1 + 2 + 3 + ... + 998) + 999

Trong ngoặc có 998 số

Tổng số đầu và số cuối là 999 + 1 = 999

Trong phép cộng có 499 cặp

Vậy tổng các số trong ngoặc là: 499 . 999 = 498510

Vậy tổng của S1 = 498510 + 999 = 499500

b: Số số hạng là:

(1001-21):2+1=491

Tổng là:

\(\dfrac{\left(1001+21\right)\cdot491}{2}=250901\)

\(=\dfrac{5}{21}+\dfrac{16}{21}-\left(\dfrac{19}{23}+\dfrac{4}{23}\right)+\dfrac{1}{2}=\dfrac{1}{2}\)

\(\dfrac{16}{21}+\dfrac{4}{23}+\dfrac{5}{21}-\dfrac{4}{23}-\dfrac{5}{21}\)

\(=\left(\dfrac{16}{21}+\dfrac{5}{21}-\dfrac{5}{21}\right)+\left(\dfrac{4}{23}-\dfrac{4}{23}\right)\)

\(=\dfrac{16}{21}+0+0\)

\(=\dfrac{16}{21}\)

\(\dfrac{16}{21}+\dfrac{4}{23}+\dfrac{5}{21}-\dfrac{4}{23}-\dfrac{5}{21}\)

\(=\left(\dfrac{16}{21}+\dfrac{5}{21}-\dfrac{5}{21}\right)+\left(\dfrac{4}{23}-\dfrac{4}{23}\right)\)

\(=\left(\dfrac{16+5-5}{21}\right)+\left(\dfrac{4-4}{23}\right)\)

\(=\dfrac{16}{21}+0\)

\(=\dfrac{16}{21}\)

= 5/2

\(\text{∘ Ans}\)

`A =`\(\left(\dfrac{27}{23}+\dfrac{1}{2}\right)-\left(\dfrac{5}{21}+\dfrac{4}{23}\right)-\dfrac{37}{21}\)

`=`\(\dfrac{27}{23}+\dfrac{1}{2}-\dfrac{5}{21}-\dfrac{4}{23}-\dfrac{37}{21}\)

`=`\(\left(\dfrac{27}{23}-\dfrac{4}{23}\right)+\left(-\dfrac{5}{21}-\dfrac{37}{21}\right)+\dfrac{1}{2}\)

`=`\(\dfrac{23}{23}-\dfrac{42}{21}+\dfrac{1}{2}=1-2+0,5=1-1,5=-0,5\)

-0,5

A) =(5+(-15))+(9+(-19))+(-11)+(13+17)+(21+(-23))

=(-10)+(-10)+(-11)+20+(-2)

=((-10)+(-10))+(-11)+(-2)+20

=(-20)+(-11)+20+(-2)

=((-20)+20)+((-11)+(-2))

=0+(-13)=-13

B) doi ti !!!!! Tich cho mik nha