) Rat nhi6u bzur dI nhdm khi dua ra d6nh giii: Do a < 4 ndn a(3 2b < 4(3 2b (l
Nhu vAy didm ntmg binh critt ctic h(tc sinlr trottg nlfim L l[t 2,]5 didm.
c) Xdc suir dd An thi d6 li
P(X>- 25) = P(X = 29) + P(X= 36) + P(X= 43) + P(X= 50; = g.ggj-5.
\ray ti l€ hoc sinh cuar nh6nr l thi d6 le 0,3-5q;. 3
Ta c6 biing tcing ket sau dA.v
K€i quA thi
cia nh6m A
Phuong 6n thi tr6c nghidm
Khong tri didm cAu sai I\'16i cAu sai tri I didm M6.i cau sai tri 2 didm
Ti le didm 0 5,63Vo 24,34Vo 52,5Vo
Ti Ie d6 nhdm 7,817o t.9770 0,35Vo
Didm trung binh t2.5 6,31 2,7 5
MOt c6ch kh6c, cid lam giim xdc sudt sai ldm trong thi TN le tang phuong 6n lua chon trons n-r6i cdu h6i. Nhidu nu6c trOn the gidi trcng bdi thi TN thurrng c6 5 phuong 6n lua chon).
finei to6n 4. Giti stlr d€ thi rrdc nghi€m cd l0 ciu hdi, m6i cdrt cd 5 ddp dn trci ldi n'ong d6 chi c6 | ddp ltn dilng. Mdi cirtt trti ldi dting drctc 5
didm, m6i cdu trci ldi sai dqc 0 didm.Thi sinh sd
d6 nii dat ir nhdt 25 didm. Hdy rinh
a)Ti lA lnc sinh ctia nh6m L bi didm 0.
b) Didm trung binh cia cdc hoc sinh trong nlrum L,.
c)Ti l€ hoc sinlt cila nh(tm L thi d6.
Ldi gidi. Chon m6t hoc sinh bdt ki trong nh6m A. Giri sr] hoc sinh du-o. c chon tdn llL An. Theo gii thiet v6i m6i cAu, xdc sudt dd An chon ddng li 0,2 vh chon sai le 0,8.
Bang lap luan tuong tu nhu bdi to6n 2 ta co
ket qui sau dAy.
a) Xric suat cld An nhAn ciiem 0l) 10.08)r" = 0,1073.
Vay ti l0 hoc sinh trong nh6m A bi didm 0 la lA,l3o/a.
b) P(X =5k)=Cfn(O,z)t.(0,8)'n-o . TU d6ta c6 bing phAn bo x6c suar cua X nhu sau: ta c6 bing phAn bo x6c suar cua X nhu sau:
/l 30 35 4A 45 50
P 0,006 1,00081 0.000 0.0000 0"0000
Bdng 7
Tr) bring 7 suy ra ki vong E(X) = 10.
Nhu vAy didm mrng binh cti.er ccic hoc sinlr rrong nhint L ld 10 didm.
c) Xiic sult cic An thi d6 la
P(X>-25) = P(X=25) + P(X= 30) + P(X= 3-5) +
P(X= 40) + P(X= 45') + P(X= 50) = 6,6323. VQ"v ril( lnc sirth cfia rth6ntL rkidd lii3,287a.J
Ta. c6 b6ng tdng ket sau d6y
Bay gid x6t phuong 6n thi TN trong d6 dd thi c6 10 cAu h6i, m6i cAu c6 5 dr{p r{n tra Ioi
trong d6 chi c6 mOt ddp dn drlng. M6i cAu
dring duoc c6ng 5 didm, m6i cAu sai bi trir a
didm (c e {1 ; 2}). Didm cuoi cirng ghi tr'6n
bli cua hoc sinh llL X= max{0, I}, trong c16
I'li didm thuc cria hoc sinh. Thi sinh thi d6
neu dat it nhdt 25 didm.
Mdi c6c ban tu phdt bidu vh gidi bhi to6ntuong tu nhu b)ri to6n 3 6 trcn.