Question

1.найдите значение выражения : 8-4,2: (2 5\14-1 4\21)= 2.решите уровнение: 1,2+3\10 y =8\15y+0,78

Answer 1

$1)$

$8-4,2:(2 \frac{5}{14}-1 \frac{4}{21} )=8-4,2:(2 \frac{15}{42}-1 \frac{8}{42})=8-4,2:1 \frac{7}{42}=$$8-4,2:1 \frac{1}{6}=8- \frac{42}{10} * \frac{6}{7} =8- \frac{36}{10}=8-3,6=4,4$

$2)$
$1,2+ \frac{3}{10}y= \frac{8}{15}y+0.78$

$\frac{3}{10}y- \frac{8}{15}y=0.78 -1.2$

$\frac{9}{30}y- \frac{16}{30}y=-0.42$

$- \frac{7}{30}y=- \frac{21}{50}$

$\frac{7}{30}y= \frac{21}{50}$

$y= \frac{21}{50}* \frac{30}{7}$

$y= \frac{9}{5}$

$y=1.8$

ответ: $1,8$

Answer 2

2 5/14-1 4/21 = 7/6
4 2/10=4 1/5:7/6=3 3/5=3,6
8-3,6=4,4

2.
3/10 у-8/15 у = 0,78-1,2
-7/30у=- 0,42=-42/100
у= 42/100:7/30=42/100*30/7=42*30/100*7=1,8