$\text{a) 47,54+18,72-17,54+7,28}$
$⇒(47,54-17,54)+(18,72+7,28)$
$⇒30+26$
$=56$
$\text{b)$\dfrac{72×64×14}{36×88×21}$}$
$\text{⇒$\dfrac{36×2×8×8×7×2}{36×8×11×7×3}$}$
$\text{⇒$\dfrac{2×8×2}{11×3}$}$
$\text{⇒$\dfrac{32}{33}$}$
$\text{c)$\dfrac{(0,25×140)×(154×0,1)×(121,5×100)}{(140÷0,4)×(154÷10)×(121,5÷0,01}$}$
$\text{⇒=$\dfrac{(140÷0,4)×(154÷10)×(121,5÷0,01}{(140÷0,4)×(154÷10)×(121,5÷0,01}$}$
$\text{⇒=1}$
