mai mình thi rồi, các bạn giúp mình với
Câu 4:
d) Ta có: \(\dfrac{-2}{17}+\dfrac{3}{19}+\dfrac{-15}{17}+\dfrac{16}{19}+\dfrac{5}{6}\)
\(=\left(-\dfrac{2}{17}-\dfrac{15}{17}\right)+\left(\dfrac{3}{19}+\dfrac{16}{19}\right)+\dfrac{5}{6}\)
\(=-1+1+\dfrac{5}{6}=\dfrac{5}{6}\)
Câu 3:
a,\(\dfrac{12}{36}\) và \(\dfrac{16}{20}\)
\(\dfrac{12}{36}=\dfrac{1}{3}\)
\(\dfrac{-16}{20}=\dfrac{-4}{5}\)
*Tìm BCNN của 3 và 5 (tự tìm)
MC: 15
\(\dfrac{1}{3}=\dfrac{1.5}{3.5}=\dfrac{5}{15}\)
\(\dfrac{-4}{5}=\dfrac{\left(-4\right).3}{5.3}=\dfrac{-12}{15}\)
\(\Rightarrow\dfrac{5}{15}\) và \(\dfrac{-12}{15}\)
b,\(\dfrac{21}{105}\) và \(\dfrac{35}{150}\)
\(\dfrac{21}{105}=\dfrac{1}{5}\)
\(\dfrac{35}{150}=\dfrac{7}{30}\)
Vì 30\(⋮\)5
\(\Rightarrow\) MC: 30
\(\dfrac{1}{5}=\dfrac{1.6}{5.6}=\dfrac{6}{30}\)
\(\Rightarrow\dfrac{6}{30}\) và \(\dfrac{7}{30}\)
Câu 4
a,\(\dfrac{3}{10}+\dfrac{5}{10}=\dfrac{8}{10}=\dfrac{4}{5}\)
b, (-27) . 36+ 64 . (-27) + 23 . (-100)
= (-27) . (36 + 64) + 23 . (-100)
= (-27) . 100 + 23 . (-100)
= 27 . (-100) + 23 . (-100)
= (-100) . (27 + 23)
= (-100) . 50
= -5000
c,\(\dfrac{5}{8}+\dfrac{3}{12}=\dfrac{5}{8}+\dfrac{1}{4}=\dfrac{5}{8}+\dfrac{2}{8}=\dfrac{7}{8}\)
d,\(\dfrac{-2}{17}+\dfrac{3}{19}+\dfrac{-15}{17}+\dfrac{16}{19}+\dfrac{5}{6}=\left(\dfrac{-2}{17}+\dfrac{-15}{17}\right)+\left(\dfrac{3}{19}+\dfrac{16}{19}\right)+\dfrac{5}{6}=-1+1+\dfrac{5}{6}=0+\dfrac{5}{6}=\dfrac{5}{6}\)
