Question

Tính Nhanh:    b)(13/21*7/8-12/21*7/8)*12      c)  7/11+3/4+4/11+8/17+1/4+18/34

Answer 1

b)\(\left(\dfrac{13}{21}\times\dfrac{7}{8}-\dfrac{12}{21}\times\dfrac{7}{8}\right)\times12\)

 =\(\left(\dfrac{7}{8}\times\left(\dfrac{13}{21}-\dfrac{12}{21}\right)\right)\times12\)

=\(\left(\dfrac{7}{8}\times\dfrac{1}{21}\right)\times12\)

=\(\dfrac{7}{16}\)

c)\(\dfrac{7}{11}+\dfrac{3}{4}+\dfrac{4}{11}+\dfrac{8}{17}+\dfrac{1}{4}+\dfrac{18}{34}\) 

= \(\left(\dfrac{7}{11}+\dfrac{4}{11}\right)+\left(\dfrac{3}{4}+\dfrac{1}{4}\right)+\dfrac{8}{17}+\dfrac{9}{17}\)

= 1 + 1 + \(\left(\dfrac{8}{17}+\dfrac{9}{17}\right)\)

= 2 + 1 

= 3