katrina decided to randomly guess at the matching section on a recent test.There were 7 questions an

Mathematics
Tutor: None Selected Time limit: 1 Day

katrina decided to randomly guess at the matching section on a recent test.There were 7 questions and 10 answers to choose from. If each answer could only be used once what is the probability that Katrina guessed correctly? 

May 26th, 2015

For each question there is only one correct answer and remaining 9 are incorrect... also each answer is used once...

Hence probability of getting correct answer for Question 1 = 1/10

Now there are 9 answers available hence probability of getting correct answer for Question 2 = 1/9

again there are 8 answers available hence probability of getting correct answer for Question 3 = 1/8

 7 answers available hence probability of getting correct answer for Question 4 = 1/7

 6 answers available hence probability of getting correct answer for Question 5 = 1/6

5 answers available hence probability of getting correct answer for Question 5= 1/5

4 answers available hence probability of getting correct answer for Question 6= 1/4

3 answers available hence probability of getting correct answer for Question 7= 1/3

hence Probability of getting all correct answers = 1/9 *1/8*1/7 *1/6*1/5*1/4*1/3 =1/181440   (Answer)

May 26th, 2015

Are you sure it's not 1/604800?

May 26th, 2015

10*9*8*7*6*5*4*3 =1814400

hence Answer must be 1/1814400     (Please correct it One zero is missing in my earlier answer)

HOw are you getting this 1/ 604800    ???

May 26th, 2015

I stopped at 4. You put 1/6 AND 1/5 for Question 5. Shouldn't we only be multiplying 7 numbers? Or 8? I did 10*9*8*7*6*5*4

May 26th, 2015

oh ... 

There are only 7 questions to be answered hence 10*9*8*7*6*5*4 is correct

I am sorry ... some mistake happened

you are correct Answer is 1/604800    But logic is same as I told above

10 options for Q 1, 9 Options for 2  & so on ..........

May 26th, 2015

Thank you so much. You helped a lot! :-)

May 26th, 2015

Please best me with a good comment about my services

May 26th, 2015

Will do :-)

May 26th, 2015

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