$\dfrac{1}{2}$+$\dfrac{1}{3}$+$\dfrac{1}{4}$+$\dfrac{12}{12}$+$\dfrac{12}{24}$+$\dfrac{12}{18}$+$\dfrac{12}{16}$
=$\dfrac{1}{2}$+$\dfrac{1}{3}$+$\dfrac{1}{4}$+$1^{}$+$\dfrac{1}{2}$+$\dfrac{2}{3}$+$\dfrac{3}{4}$
=($\dfrac{1}{2}$+$\dfrac{1}{2}$)+($\dfrac{1}{3}$+$\dfrac{2}{3}$)+($\dfrac{1}{4}$+$\dfrac{3}{4}$)+$1^{}$
=$1^{}$+$1^{}$+$1^{}$+$1^{}$
=$4^{}$
CHO MK CTLHN NHA:((
