Question

А)2/7y+5/14y+10/21y
в)7/12m+1/6m-2/3m
c)y-(8/15y+5/12y)

Answer 1

( а )

$\frac{2}{7}y+\frac{5}{14}y+\frac{10}{21}y=\frac{2*6}{7*6}y+\frac{5*3}{14*3}y+\frac{10*2}{21*2}y=\frac{12}{42}y+\frac{15}{42}y+\frac{20}{42}y=\\\\=\frac{27}{42}y+\frac{20}{42}y=\frac{47}{42}y= 1\frac{5}{42}y$

( в )

$\frac{7}{12}m+\frac{1}{6}m-\frac{2}{3}m=\frac{7}{12}m+\frac{1*2}{6*2}m-\frac{2*4}{3*4}m= \frac{7}{12}m+\frac{2}{12}m-\frac{8}{12}m=\frac{9}{12}m-\frac{8}{12}m=\frac{1}{12}m$

( с )

$y-(\frac{8}{15}y+\frac{5}{12}y)=\frac{1}{1}y-(\frac{8*4}{15*4}y+\frac{5*5}{12*5}y)=\frac{1*60}{1*60}y-(\frac{32}{60}y+\frac{25}{60})=\\\\=\frac{60}{60}y-\frac{57}{60}y=\frac{3}{60}y=\frac{1}{20}y$