x*0.4=y*0.3,所以x:y=3:4,甲是乙的3/4,甲比乙少1/4.
a设为x,b就是4x/5,c就是4x/6,x-4x/6=15,x=45
(1+12)*(1-12)*(1+13)*(1-13)*...*(1+112)*(1-112)=[(1+12)*(1+13)*...*(1+112)]*[(1-12)*(1-13)*...*(1-112)]=(3/2*4/3*.*13/12)*(1/2*2/3*.*11/12)=13/2*1/12=13/24
x*0.4=y*0.3,所以x:y=3:4,甲是乙的3/4,甲比乙少1/4.
a设为x,b就是4x/5,c就是4x/6,x-4x/6=15,x=45
(1+12)*(1-12)*(1+13)*(1-13)*...*(1+112)*(1-112)=[(1+12)*(1+13)*...*(1+112)]*[(1-12)*(1-13)*...*(1-112)]=(3/2*4/3*.*13/12)*(1/2*2/3*.*11/12)=13/2*1/12=13/24