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a: Thay a=9 và b=15 vào P, ta được:
\(P=\left(9+1\right)\cdot2+\left(15+1\right)\cdot3\)
\(=10\cdot2+16\cdot3=20+48=68\)
b: \(m=2\cdot a+3\cdot b+5=2\cdot9+3\cdot15+5=68\)
mà P=68
nên P=m
`1/2 xx 1/3 + 1/4 = 1/6 + 1/4 = 4/24 + 6/24 = 10/24 = 5/12`
\(\dfrac{1}{2}\times\dfrac{1}{3}+\dfrac{1}{4}=\dfrac{1\times1}{2\times3}+\dfrac{1}{4}=\dfrac{1}{6}+\dfrac{1}{4}=\dfrac{2+3}{12}=\dfrac{5}{12}\)
\(\dfrac{1}{2}\) x \(\dfrac{1}{3}\) : \(\dfrac{1}{4}\)
= \(\dfrac{1}{6}\) : \(\dfrac{1}{4}\)
= \(\dfrac{1}{6}\) x \(\dfrac{4}{1}\)
= \(\dfrac{4}{6}\)
= \(\dfrac{2}{3}\)
\(\dfrac{11}{2}\): \(\dfrac{1}{4}\) \(\times\) \(\dfrac{5}{3}\)
= \(\dfrac{11}{2}\) \(\times\) \(\dfrac{4}{1}\) \(\times\) \(\dfrac{5}{3}\)
= 22 \(\times\) \(\dfrac{5}{3}\)
= \(\dfrac{110}{3}\)
\(\dfrac{5}{2}-\dfrac{1}{4}+\dfrac{5}{3}\)
= \(\dfrac{30}{12}-\dfrac{3}{12}+\dfrac{20}{12}\)
= \(\dfrac{7}{12}\)
\(\dfrac{14}{5}\times\dfrac{2}{3}\)+ 5
= \(\dfrac{28}{15}\) + 5
= \(\dfrac{28}{15}\) + \(\dfrac{75}{15}\)
= \(\dfrac{103}{15}\)
\(\dfrac{5}{2}+\dfrac{1}{4}.\dfrac{1}{8}\)
\(=\dfrac{5}{2}+\dfrac{1}{32}=\dfrac{5.16+1}{32}=\dfrac{80+1}{32}=\dfrac{81}{32}\)
\(\dfrac{5}{2}\) + \(\dfrac{1}{4}\) x \(\dfrac{1}{8}\)
= \(\dfrac{5}{2}\) + \(\dfrac{1}{32}\)
= \(\dfrac{80}{32}\) + \(\dfrac{1}{32}\)
= \(\dfrac{81}{32}\)