Question

TÍNH NHANH 

a)15x14-1

   13x15+14

b)9x(262626+88888)

        272727  99999

c)1+2+3+4+5+6+7+8+9

              10

d)4343+4343+4343+4343

  7171 7171 7171 7171

bài phân số

Answer 1

a, \(\dfrac{15\times14-1}{13\times15+14}\)

 = \(\dfrac{15\times\left(13+1\right)-1}{13\times15+14}\) 

= \(\dfrac{13\times15+15-1}{13\times15+14}\) 

= \(\dfrac{13\times15+14}{13\times15+14}\)

= 1

Answer 2

c, \(\dfrac{1+2+3+4+5+6+7+8+9}{10}\)

= \(\dfrac{\left(9+1\right)\times\left\{\left(9-1\right):1+1\right\}:2}{10}\)

= \(\dfrac{10\times9:2}{10}\)

= \(\dfrac{9}{2}\)