$\boxed{\text{Câu 4:}}$

`P(A)=1/8; P(B)=2/7`

`a)`

`A,B` là hai biến cố xung khắc.

`=>P(A nn B)=0`

`=>P(A uu B)=P(A)+P(B)=1/8+2/7=23/56`

`b)`

`P(A uu B)=P(A)+P(B)-P(A nn B)`

`=1/6+1/5-1/20`

`=19/60`

$\boxed{\text{Câu 5:}}$

`a)`

`P(A nn B)=P(A). P(B)=1/5. 8/9=8/45=m/n`

`=>{(m=8),(m=45):}`

`=>m+n=8+45=53`

`b)`

`P(A uu B)=P(A)+P(B)-P(A nn B)`

`=> 1/2=4/5+5/6-P(A nn B)`

`=>P(A nn B)=17/15=m/n`

`=>{(m=17),(n=15):}`

`=>m+n=17+15=32`