$a)$ $\genfrac{}{}{0ex}{}{4}{9}+\genfrac{}{}{0ex}{}{1}{4}=\genfrac{}{}{0ex}{}{16}{36}+\genfrac{}{}{0ex}{}{9}{36}=\genfrac{}{}{0ex}{}{25}{36}$.

$b)$ $\genfrac{}{}{0ex}{}{1}{3}.\left(\genfrac{}{}{0ex}{}{-4}{5}\right)+\genfrac{}{}{0ex}{}{1}{3}.\genfrac{}{}{0ex}{}{-1}{5}+2023^0$

$=\genfrac{}{}{0ex}{}{1}{3}.(\genfrac{}{}{0ex}{}{-4}{5}+\genfrac{}{}{0ex}{}{-1}{5})+1$

$=\genfrac{}{}{0ex}{}{1}{3}.(-1)+1$

$=-\genfrac{}{}{0ex}{}{1}{3}+1=\genfrac{}{}{0ex}{}{2}{3}$.

$c)$ $\genfrac{}{}{0ex}{}{1}{5}-[\genfrac{}{}{0ex}{}{1}{4}-(1-\genfrac{}{}{0ex}{}{1}{2}{)}^2]$.

$=\genfrac{}{}{0ex}{}{1}{5}-[\genfrac{}{}{0ex}{}{1}{4}-(\genfrac{}{}{0ex}{}{1}{2}{)}^2]$

$=\genfrac{}{}{0ex}{}{1}{5}-[\genfrac{}{}{0ex}{}{1}{4}-\genfrac{}{}{0ex}{}{1}{4}]$

$=\genfrac{}{}{0ex}{}{1}{5}-0=\genfrac{}{}{0ex}{}{1}{5}$
 

$a)$ $\genfrac{}{}{0ex}{}{4}{9}+\genfrac{}{}{0ex}{}{1}{4}=\genfrac{}{}{0ex}{}{16}{36}+\genfrac{}{}{0ex}{}{9}{36}=\genfrac{}{}{0ex}{}{25}{36}$.

$b)$ $\genfrac{}{}{0ex}{}{1}{3}.\left(\genfrac{}{}{0ex}{}{-4}{5}\right)+\genfrac{}{}{0ex}{}{1}{3}.\genfrac{}{}{0ex}{}{-1}{5}+2023^0$

$=\genfrac{}{}{0ex}{}{1}{3}.(\genfrac{}{}{0ex}{}{-4}{5}+\genfrac{}{}{0ex}{}{-1}{5})+1$

$=\genfrac{}{}{0ex}{}{1}{3}.(-1)+1$

$=-\genfrac{}{}{0ex}{}{1}{3}+1=\genfrac{}{}{0ex}{}{2}{3}$.

$c)$ $\genfrac{}{}{0ex}{}{1}{5}-[\genfrac{}{}{0ex}{}{1}{4}-(1-\genfrac{}{}{0ex}{}{1}{2}{)}^2]$.

$=\genfrac{}{}{0ex}{}{1}{5}-[\genfrac{}{}{0ex}{}{1}{4}-(\genfrac{}{}{0ex}{}{1}{2}{)}^2]$

$=\genfrac{}{}{0ex}{}{1}{5}-[\genfrac{}{}{0ex}{}{1}{4}-\genfrac{}{}{0ex}{}{1}{4}]$

$=\genfrac{}{}{0ex}{}{1}{5}-0=\genfrac{}{}{0ex}{}{1}{5}$
 

$a)$ $\genfrac{}{}{0ex}{}{4}{9}+\genfrac{}{}{0ex}{}{1}{4}=\genfrac{}{}{0ex}{}{16}{36}+\genfrac{}{}{0ex}{}{9}{36}=\genfrac{}{}{0ex}{}{25}{36}$.

$b)$ $\genfrac{}{}{0ex}{}{1}{3}.\left(\genfrac{}{}{0ex}{}{-4}{5}\right)+\genfrac{}{}{0ex}{}{1}{3}.\genfrac{}{}{0ex}{}{-1}{5}+2023^0$

$=\genfrac{}{}{0ex}{}{1}{3}.(\genfrac{}{}{0ex}{}{-4}{5}+\genfrac{}{}{0ex}{}{-1}{5})+1$

$=\genfrac{}{}{0ex}{}{1}{3}.(-1)+1$

$=-\genfrac{}{}{0ex}{}{1}{3}+1=\genfrac{}{}{0ex}{}{2}{3}$.

$c)$ $\genfrac{}{}{0ex}{}{1}{5}-[\genfrac{}{}{0ex}{}{1}{4}-(1-\genfrac{}{}{0ex}{}{1}{2}{)}^2]$.

$=\genfrac{}{}{0ex}{}{1}{5}-[\genfrac{}{}{0ex}{}{1}{4}-(\genfrac{}{}{0ex}{}{1}{2}{)}^2]$

$=\genfrac{}{}{0ex}{}{1}{5}-[\genfrac{}{}{0ex}{}{1}{4}-\genfrac{}{}{0ex}{}{1}{4}]$

$=\genfrac{}{}{0ex}{}{1}{5}-0=\genfrac{}{}{0ex}{}{1}{5}$
 

$a)$ $\genfrac{}{}{0ex}{}{4}{9}+\genfrac{}{}{0ex}{}{1}{4}=\genfrac{}{}{0ex}{}{16}{36}+\genfrac{}{}{0ex}{}{9}{36}=\genfrac{}{}{0ex}{}{25}{36}$.

$b)$ $\genfrac{}{}{0ex}{}{1}{3}.\left(\genfrac{}{}{0ex}{}{-4}{5}\right)+\genfrac{}{}{0ex}{}{1}{3}.\genfrac{}{}{0ex}{}{-1}{5}+2023^0$

$=\genfrac{}{}{0ex}{}{1}{3}.(\genfrac{}{}{0ex}{}{-4}{5}+\genfrac{}{}{0ex}{}{-1}{5})+1$

$=\genfrac{}{}{0ex}{}{1}{3}.(-1)+1$

$=-\genfrac{}{}{0ex}{}{1}{3}+1=\genfrac{}{}{0ex}{}{2}{3}$.

$c)$ $\genfrac{}{}{0ex}{}{1}{5}-[\genfrac{}{}{0ex}{}{1}{4}-(1-\genfrac{}{}{0ex}{}{1}{2}{)}^2]$.

$=\genfrac{}{}{0ex}{}{1}{5}-[\genfrac{}{}{0ex}{}{1}{4}-(\genfrac{}{}{0ex}{}{1}{2}{)}^2]$

$=\genfrac{}{}{0ex}{}{1}{5}-[\genfrac{}{}{0ex}{}{1}{4}-\genfrac{}{}{0ex}{}{1}{4}]$

$=\genfrac{}{}{0ex}{}{1}{5}-0=\genfrac{}{}{0ex}{}{1}{5}$
 

Lớp 4A trồng được số cây là:

(600-50)  : 2 = 275 (cây)

Lớp 4B trồng được số cây là:

600 - 275= 325 (cây)