♥Awesome Probability♥
A student is not be able to remember the last digit of his private tutor's cell number at the time of urgency.Unfortunately his mobile battery is also down & his house is under the situation of power cut at that time.He could only try that cell number at most 4 times and then his mobile will be switched off.
What is the probability that he is able to dial the correct number before his mobile gets switched off?
(Give the answer as % in number e.g., if your answer is 50% then write 50)
The answer is 40.
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1 solution
It seems no one is able to provide a proper solution..So I'm providing one as a guide..;-) This problem simply lead us to find the probability of dialing one digit correctly in ATMOST 4 attempts,isn't it? Now getting the correct digit at first attempt is clearly (1/10). Getting the correct digit at second attempt is clearly (9/10) (1/9) [because 1st attempt must have been wrong!] For the same logic we'd have, getting the correct digit at third attempt is (9/10) (8/9) (1/8). And getting the correct digit at fourth attempt is (9/10) (8/9) (7/8) (1/7). Now summing all together we get the correct probability=(1/10)+(1/10)+(1/10)+(1/10) =(2/5) ♥♡♥ So its 40% . . . :-) N.B. no shorter solution mates! Because if you dare do (4)*(1/10),you'll get the answer but your logic will be purely incorrect in this particular occasion!!