Thực hiện phép tính (bằng cách hợp lí nếu có thể) a) 5/23 + 7/17 + 0,25

$=0+1+0,25=1,25$

b) $\frac{3}{7}.2\frac{2}{3}-\frac{3}{7}.1\frac{1}{2}$

$=\frac{3}{7}.\left(2\frac{2}{3}-1\frac{1}{2}\right)$

$=\frac{3}{7}.\left(\frac{8}{3}-\frac{3}{2}\right)$

$=\frac{3}{7}.\left(\frac{16}{6}-\frac{9}{6}\right)$

$=\frac{3}{7}.\frac{7}{6}=\frac{1}{2}$

c) $13\frac{1}{4}:\left(-\frac{4}{7}\right)-17\frac{1}{4}:\left(-\frac{4}{7}\right)$

$=13\frac{1}{4}.\frac{-7}{4}-17\frac{1}{4}.\frac{-7}{4}$

$=\frac{-7}{4}.\left(13\frac{1}{4}-17\frac{1}{4}\right)$

$=\frac{-7}{4}.\left(-4\right)=7$

d) $\frac{100}{123}:\left(\frac{3}{4}+\frac{7}{12}\right)+\frac{23}{123}:\left(\frac{9}{5}-\frac{7}{15}\right)$

$=\frac{100}{123}:\left(\frac{9}{12}+\frac{7}{12}\right)+\frac{23}{123}:\left(\frac{27}{15}-\frac{7}{15}\right)$

$=\frac{100}{123}:\frac{16}{12}+\frac{23}{123}:\frac{20}{15}$

$=\frac{100}{123}.\frac{12}{16}+\frac{23}{123}.\frac{15}{20}$

$=\frac{100}{123}.\frac{3}{4}+\frac{23}{123}.\frac{3}{4}$

$=\frac{3}{4}.\left(\frac{100}{123}+\frac{23}{123}\right)$

$=\frac{3}{4}.\frac{123}{123}=\frac{3}{4}.1=\frac{3}{4}$