A=1-(2/3+1/4)
2/3+1/4=
2/3=2x4/3x4=8/12
1/4=1x3/3x4=3/12
2/3+1/4=8/12+3/12=11/12
A=1-11/12
1=12/12
A=12/12-11/12=1/12
B=-2/3+5/3x2/7
B=-2/3+(5/3x2/7)
5/3x2/7=5x2/3x7=10/21
B= -2/3+10/21
-2/3=-2x7/3x7=-14/21
B=-14/21+10/21=-4/21
C= (1/3-1/5):2/5
1/3-1/5=
1/3=1x5/3x5=5/15
1/5=1x3/5x3=3/15
1/3-1/5=5/15-3/15=2/15
C=2/15:2/5=2/15x5/2=2x5/15x2=2x5/3x5x2=1/3
D+(-2/5+5/2)/(1/2-3/4)
-2/5+5/2=
-2/5=-2x2/5x2=-4/10
5/2=5x5/2x5=25/10
-2/5+5/2=-4/10+25/10=21/10
1/2-3/4=
1/2=1x2/2x2=2/4
2/4-3/4=-1/4
D=(21/10)/-1/4=21/10:-1/4=(21/10)x-4= (21x2x2)/5x2=42/5