1)30:3/5=30*5/3=50
2)(-2)*5/4*(-3)= -10/-12= 5/6
3)x/18=5/15
x=18*5/15=18/3=5
4) 64-100
x-25
x=64*25/100=16
5) 2,4463 = 2,45
-2,1345 = -2,13
6)4 3/4-(4.25- 3 1/2)= 19/4-(425/100-7/2=19/4-3/4=16/4=4
7)5-2(x-1)=4-x
5-2x+2-4+x=0
-2x+x+3=0
2x-x-3=0
D=1-4*2*(-3)=25
√D=5
x1=1-5/4=-1
x2=3/2