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Bài 2
a.8/15+7/4+7/15+5/4
=8/15+7/15+7/4+5/4
=15/15+12/4
=1+3
=4
b.98,54-(41,82-35,72)
=98,54-6,1
=92,44
\(\frac{11}{15}\cdot\frac{6}{7}+\frac{11}{15}\cdot\frac{8}{7}\)
\(=\frac{11}{15}\cdot\left(\frac{6}{7}+\frac{8}{7}\right)\)
\(=\frac{11}{15}\cdot2=\frac{22}{15}\)
Chú ý dấu " \(\cdot\) " là dấu nhân
a.8/15+7/4+7/15+5/4
=8/15+7/15+7/4+5/4
=15/15+12/4
=1+3=4
b.98,54-(41,82-35,72)
=98,54-6,1
=92,44
\(5\dfrac{3}{4}:3+2\dfrac{1}{4}\times\dfrac{1}{3}-\dfrac{1}{8}=\left(5\dfrac{3}{4}+2\dfrac{1}{4}\right)\times\dfrac{1}{3}-\dfrac{1}{8}\\ =8\times\dfrac{1}{3}-\dfrac{1}{8}=\dfrac{8}{3}-\dfrac{1}{8}=\dfrac{61}{24}\\ ----\\ \dfrac{3}{5}:\dfrac{5}{6}:\dfrac{6}{7}:\dfrac{7}{8}+\dfrac{2}{5}+\dfrac{23}{35}\\ =\dfrac{3}{5}\times\dfrac{6}{5}\times\dfrac{7}{6}\times\dfrac{8}{7}+\dfrac{2}{5}+\dfrac{23}{35}=\dfrac{18}{25}\times\dfrac{4}{3}+\dfrac{2}{5}+\dfrac{23}{35}=\dfrac{353}{175}\)
(2/7+5/7)+4/9=1+4/9=13/9
17/11+(7/15+5/11)=17/11+7/15+5/11=(17/11+5/11)+7/15=2+5/11=27/11
(19+1)+(18+2)+(17+3)+(16+4)+(15+5)+(14+6)+(13+7)+(12+8)+(11+9)+20)+10
=20+20+20+20+20+20+20+20+20+20=(20*10)+10
=210
1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20
=(1+19)+(2+18)+(3+17)+(4+16)+(5+15)+(6+14)+(7+13)+(8+12)+(9+11)+(10+20)
=20+20+20+20+20+20+20+20+20+30
=(20 x 9) + 30
=180 + 30
=210
tk nha
