<span>x-2 1/3=5 2/7
x=2 1/3+5 2/7
x=2 7/21+5 6/21
x=7 13/21
</span>
<span>1) 5а+(-8в)+(-7с)+(-2а)+3в+с=5а-8в-7с-2а+3в+с=3а-5в-6с
</span><span>2) 3n+6m+(-15k)+(-n)+(-5m)+8k=3n+6m-15k-n-5m=2n+m-15k
</span><span>3) 8.2a+-(4b)+10.3c+(-4a)+(-9.5b)+(-8c)=8.2a-4b+10.3c-4a-9.5b-8c=4.2a-13.5b+2.3c</span>
13/18х-7/30=3/10х+1/12
13/18х-3/10х=7/30+1/12
65/90х-27/90х=14/60+5/60
38/90х=19/60
х=19/60:38/90
х=19/60*90/38
х=3/4
54/3=18-листов в 1 тетради.
90*18=1620-
72*18=1296