Question

Tính bằng cách thuận tiện nhất 

a) 3/7+5/2+4/7=

b) 6/8+4/5+1/4=

c) 21/34+4/9+7+17=

Answer 1

a; \(\dfrac{3}{7}\) + \(\dfrac{5}{2}\) + \(\dfrac{4}{7}\)

= (\(\dfrac{3}{7}+\dfrac{4}{7}\)) + \(\dfrac{5}{2}\)

= 1 + \(\dfrac{5}{2}\)

= \(\dfrac{2}{2}+\dfrac{5}{2}\)

=  \(\dfrac{7}{2}\)

Answer 2

b; \(\dfrac{6}{8}\) + \(\dfrac{4}{5}\) + \(\dfrac{1}{4}\) 

= \(\dfrac{1}{4}\) + \(\dfrac{4}{5}\) + \(\dfrac{1}{4}\)

= (\(\dfrac{1}{4}\) + \(\dfrac{1}{4}\)) + \(\dfrac{4}{5}\)

= \(\dfrac{2}{4}\) + \(\dfrac{4}{5}\)

= \(\dfrac{1}{2}\) + \(\dfrac{4}{5}\)

= \(\dfrac{5}{10}\) + \(\dfrac{8}{10}\)

= \(\dfrac{13}{10}\)

Answer 3

c; \(\dfrac{21}{34}\) + \(\dfrac{4}{9}\) + 7 + 17

= (\(\dfrac{21}{34}\) + \(\dfrac{4}{9}\)) + (7 + 17)

= \(\dfrac{325}{306}\) + 24

= \(\dfrac{7669}{306}\)