Question

Tính bằng cách thuận tiện nhất:

2/5+3/4+1/4=............................................................................................................

30/4-6/8-15/20=.....................................................................................................

Answer 1

\(a,=\dfrac{2}{5}+\left(\dfrac{3}{4}+\dfrac{1}{4}\right)=\dfrac{2}{5}+\dfrac{4}{4}=\dfrac{2}{5}+1=\dfrac{2+5}{5}=\dfrac{7}{5}\\ -------------\\ b,=\left(\dfrac{30}{4}-\dfrac{15}{20}\right)-\dfrac{6}{8}=\left(\dfrac{30.5-15}{20}\right)-\dfrac{6}{8}=\dfrac{27}{4}-\dfrac{6}{8}=\dfrac{27.2-6}{8}=\dfrac{54-6}{8}=\dfrac{48}{8}=6\)

Answer 2

`2/5 + 3/4 + 1/4= 2/5 + ( 3/4+1/4)= 2/5 + 4/4= 2/5 + 1= 2/5+ 5/5= 7/5`

`30/4-6/8-15/20= 30/4- 3/4 -15/20= 27/4- 15/20= 135/20- 15/20= 6`

Answer 3

2/5 + 3/4 + 1/4= 2/5 + (3/4 + 1/4) = 2/5 + 1 = 2/5 +5/5 = 7/5

30/4 - 6/8 - 15/ 20 = 30/4 - 3/4 - 3/4= 24/4 = 6

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