1)(800-а):20
а=80
(800-80):20=720:20=36
2)(405-25)+b*31
b=20
(405-25)+20*31=380+620=1000
11/12 -2/3+3/4= 11/12-8/12+9/12= 12/12=1
<span>24+42= 12*2 + 21*2= 2*(12+11)=2*33
20+20+20=3*20=60</span>
<span>А:5+70=120
</span><span>А:5=120-70
</span><span>А:5=50
А=50*5
А=250
-----------------
250:5+70=120
120=120</span>
1)325:65=5
2)325:5=65
проверка: 65•5=325