1/2 + 1/3=(1*3+1*2)/2*3=(3+2)/6=5/6
1/3+1/4= (1*4+1*3)/3*4=7/12
1/4+2/3+1/12=(1*3+2*4+1)/12=(3+8+1)/12=12/12=1
1/3+3/4+5/21=(1*28+3*21+5*4)/84=(28+63+20)/84=111/84=37/28
7/12+5/18+1/24=(7*6+5*4+1*3)/72=(42+20+3)/72=65/72
1/3+2/3² +10/3²=(1*3+2+10)/9=15/9=5/3