Question

[Thầy Đức Anh]

Tính giá trị các biểu thức sau theo cách hợp lí nhất.
a) $A=\left(\dfrac{1}{3}-\dfrac{8}{15}-\dfrac{1}{7}\right)+\left(\dfrac{2}{3}+\dfrac{-7}{15}+1 \dfrac{1}{7}\right)$;
b) $\mathrm{B}=0,25+\dfrac{3}{5}-\left(\dfrac{1}{8}-\dfrac{2}{5}+1 \dfrac{1}{4}\right)$.

Answer 1

[Phạm Trường Giang]

a) $A=\left(\frac{1}{3}+\frac{2}{3}\right)-\left(\frac{8}{15}+\frac{7}{15}\right)+\left(\frac{-1}{7}+1\frac{1}{7}\right)=1-1+1=1$;
b) $B=\left(0.25-1\frac{1}{4}\right)+\left(\frac{3}{5}+\frac{2}{5}\right)-\frac{1}{8}$
$=\left(\frac{1}{4}-1-\frac{1}{4}\right)+1-\frac{1}{8}=\frac{-1}{8}$.

Answer 2

[TINH]

a) $A=\left(\genfrac{}{}{0ex}{}{1}{3}+\genfrac{}{}{0ex}{}{2}{3}\right)-\left(\genfrac{}{}{0ex}{}{8}{15}+\genfrac{}{}{0ex}{}{7}{15}\right)+\left(\genfrac{}{}{0ex}{}{-1}{7}+1\genfrac{}{}{0ex}{}{1}{7}\right)=1-1+1=1$ b) $\mathrm{B}=\left(0.25-1\genfrac{}{}{0ex}{}{1}{4}\right)+\left(\genfrac{}{}{0ex}{}{3}{5}+\genfrac{}{}{0ex}{}{2}{5}\right)-\genfrac{}{}{0ex}{}{1}{8}$
$=\left(\genfrac{}{}{0ex}{}{1}{4}-1-\genfrac{}{}{0ex}{}{1}{4}\right)+1-\genfrac{}{}{0ex}{}{1}{8}=\genfrac{}{}{0ex}{}{-1}{8}$.