Giải thích các bước giải:
$a)6,75×4,2$
C1:$=\dfrac{ 675}{100}×\dfrac{42}{10}$
$=\dfrac{27}{4}×\dfrac{21}{5}$
$=\dfrac{567}{20}$
$=28,35$
C2:$=6,75×4+6,75×0,2$
$=27+1,35$
$=28,35$
$b)3,25×4,2$
C1:$=\dfrac{ 325}{100}×\dfrac{42}{10}$
$=\dfrac{13}{4}×\dfrac{21}{5}$
$=\dfrac{273}{20}$
$=13,65$
C2:$=3,25×4+3,25×0,2$
$=13+0,65$
$=13,65$
Học tốt!!!