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NCERT Class XI Mathematics - Probability - Solutions
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Question : 31 of 54
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Three coins are tossed once. Find the probability of getting (i) 3 heads (ii) 2 heads (iii) atleast 2 heads (iv) atmost 2 heads (v) no head (vi) 3 tails (vii) exactly two tails (viii) no tail (ix) atmost two tails
Solution:
An experiment consists of tossing 3 coins ∴ The sample space of the given experiment is given by S = {HHH, HHT, HTH, THH, TTH, THT, HTT, TTT} ∴ n(S) = 8 (i) Let E be the event that 3 heads appear ∴ n(E) = 1 (Since E = {HHH}) ⇒ P (E) = = (ii) Let E be the event that 2 heads appear ∴ n(E) = 3 (Since E = {HHT, HTH, THH}) ⇒ P (E) = = (iii) Let E be the event that atleast 2 heads appear ∴ n(E) = 4 (Since E = {HTH, HHT, THH, HHH}) ⇒ P (E) = = = (iv) Let E be the event that at most 2 heads appear ∴ n(E) = 7 [Since E = HHT, HTH, THH, TTT, THT, TTH, HTT] ⇒ P (E) = = (v) Let E be the event that no head appears ∴ n(E) = 1 (Since E = {TTT}) ⇒ P (E) = = (vi) Let E be the event that 3 tails appear ∴ n(E) = 1 (Since E = {TTT}) ⇒ P (E) = = (vii) Let E be the event that exactly two tails appear ∴ n(E) = 3 (Since E = {TTH, THT, HTT}) ⇒ P (E) = = (viii) Let E be the event that no tail appears ∴ n(E) = 1 (Since E = {HHH}) (ix) Let E be the event that atmost two tails appear ∴ n(E) = 7 (Since E = {THH, HTH, HHT, HTT, THT, TTH, HHH}) ⇒ P (E) = =
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