Question Number 40550 by vajpaithegrate@gmail.com last updated on 24/Jul/18
$$\mathrm{if}\:\mathrm{three}\:\mathrm{numbers}\:\mathrm{are}\:\mathrm{drawn}\:\mathrm{at}\:\mathrm{random} \\ $$$$\mathrm{successively}\:\mathrm{without}\:\mathrm{replacement}\:\mathrm{from} \\ $$$$\mathrm{a}\:\mathrm{set}\:\mathrm{S}=\left\{\mathrm{1},\mathrm{2},……\mathrm{10}\right\}\mathrm{then}\:\mathrm{probability}\:\mathrm{that} \\ $$$$\mathrm{the}\:\mathrm{minimum}\:\mathrm{of}\:\mathrm{the}\:\mathrm{choosen}\:\mathrm{number}\:\mathrm{is} \\ $$$$\mathrm{3}\:\mathrm{or}\:\mathrm{their}\:\mathrm{maximum}\:\mathrm{is}\:\mathrm{7}\:\:\:\:\:\:\:\: \\ $$$$\:\mathrm{Answer}=\frac{\mathrm{11}}{\mathrm{40}} \\ $$
Answered by tanmay.chaudhury50@gmail.com last updated on 24/Jul/18
$${P}\left({A}\right)={probablity}\:{to}\:{choose}\:{three}\:{number} \\ $$$${where}\:\mathrm{3}\:{is}\:{minimum} \\ $$$${so}\:{choosing}\:\mathrm{3}\:{and}\:{any}\:{two}\:{number}\:{from}\left(\mathrm{4},\mathrm{5},\right. \\ $$$$\left.\mathrm{6},\mathrm{7},\mathrm{8},\mathrm{9},\mathrm{10}\right) \\ $$$${P}\left({A}\right)\frac{\mathrm{1}{c}_{\mathrm{1}} ×\mathrm{7}{c}_{\mathrm{2}} }{\mathrm{10}{c}_{\mathrm{3}} }=\frac{\mathrm{1}×\frac{\mathrm{7}×\mathrm{6}}{\mathrm{2}}}{\frac{\mathrm{10}×\mathrm{9}×\mathrm{8}}{\mathrm{3}×\mathrm{2}}}=\frac{\mathrm{21}}{\mathrm{120}}=\frac{\mathrm{7}}{\mathrm{40}} \\ $$$${P}\left({B}\right)={probabligy}\:{to}\:{choose}\:{three}\:{number} \\ $$$${where}\:\mathrm{7}\:{is}\:{maximum} \\ $$$${so}\:{choosing}\:\mathrm{7}\:{and}\:{any}\:{two}\:{number}\:{from} \\ $$$$\left(\mathrm{1},\mathrm{2},\mathrm{3},\mathrm{4},\mathrm{5},\mathrm{6}\right) \\ $$$${P}\left({B}\right)\frac{\mathrm{1}{c}_{\mathrm{1}} ×\mathrm{6}{c}_{\mathrm{2}} }{\mathrm{10}{c}_{\mathrm{3}} }=\frac{\mathrm{15}}{\frac{\mathrm{10}×\mathrm{9}×\mathrm{8}}{\mathrm{3}×\mathrm{2}}}=\frac{\mathrm{15}}{\mathrm{120}}=\frac{\mathrm{5}}{\mathrm{40}} \\ $$$${P}\left({A}\right){orP}\left({B}\right) \\ $$$${P}\left({A}\right)\cup{P}\left({B}\right)={P}\left({A}\right)+{P}\left({B}\right)−{P}\left({A}\right)\cap{P}\left({B}\right) \\ $$$${calculaion}\:{of}\:{P}\left({A}\right)\cap{P}\left({B}\right) \\ $$$$\left(\mathrm{3},\mathrm{4},\mathrm{5},\mathrm{6},\mathrm{7}\right)\:\:\:{choosing}\:\mathrm{3}\:{and}\:\mathrm{7}\:{and}\:{any}\:{one}\:{from} \\ $$$$\left(\mathrm{4},\mathrm{5},\mathrm{6}\right) \\ $$$${P}\left({A}\right)\cap{P}\left({B}\right)=\frac{\mathrm{1}{c}_{\mathrm{1}} ×\mathrm{1}{c}_{\mathrm{1}} ×\mathrm{3}{c}_{\mathrm{1}} }{\mathrm{10}{c}_{\mathrm{3}} }=\frac{\mathrm{3}}{\mathrm{120}}=\frac{\mathrm{1}}{\mathrm{40}} \\ $$$${so}\:{required}\:{results}=\frac{\mathrm{7}}{\mathrm{40}}+\frac{\mathrm{5}}{\mathrm{40}}−\frac{\mathrm{1}}{\mathrm{40}}=\frac{\mathrm{11}}{\mathrm{40}} \\ $$
Commented by vajpaithegrate@gmail.com last updated on 25/Jul/18
$$\mathrm{tnq}\:\mathrm{sir} \\ $$