## 10_CuspofPower_10 2 years ago Teesha is in the French club. There are 31 students in the club. The French teacher will pick two students at random to guide visiting students from France. What is the probability that Teesha will be picked as a guide? Hint: Teesha must be picked first or second A. 1/30 B. 30/31 C. 1/930 D. 2/31

1. hartnn

just solved the same type of question.... http://openstudy.com/users/smokeysthename#/updates/51518fd7e4b0ae0b658be4da

2. 10_CuspofPower_10

Thank you hartnn, I'll take a look at that.

3. hartnn

welcome ^_^ if you got any doubts, ask here, we'll clarify it here itself.

4. 10_CuspofPower_10

Thank you, will do. :b

5. 10_CuspofPower_10

Mhmm Mhmm so I went and looked............ I'm extremely lost o.o lol >.<

6. hartnn

the probability that Teesha will be picked as a guide means Teesha will be picked on 1st selection AND Teesha will be picked on 2nd selection got this ?

7. 10_CuspofPower_10

Yesh

8. hartnn

i would like to revise my previous statement, the probability that Teesha will be picked as a guide means Teesha will be picked on 1st selection and NOT in 2nd(because she's already selected), AND Teesha will be picked on 2nd selection and NOT in 1st.

9. 10_CuspofPower_10

Oooooh, so what happens then?

10. hartnn

so, we'll consider 1st case, Teesha will be picked on 1st selection and NOT in 2nd(because she's already selected), 1st selection, teacher has 31 choices, to select teesha, she has 1 option, so, 1/31 2nd selection, teacher now have 30 other choices, and to NOT select teesha, she can pick any of 30 other, so 30/30 so, overall for 1st case, it'll be 1/31 *30/30 got this ?

11. 10_CuspofPower_10

I got it...... 30/930, does it need to be simplified?

12. hartnn

1/31 + 30/31*1/30 = 2/31 how you got 30/930 ??

13. 10_CuspofPower_10

Lol............ ooooooh goodness, I multiplied 1/31 *30/30 o.o

14. hartnn

ohh..for 1st case....30/30 =1 :P i though you've got the final answer.

15. hartnn

ok, did you understand 1st case ? can i move to 2nd case ?

16. 10_CuspofPower_10

17. hartnn

2nd case, Teesha will be picked on 2nd selection and NOT in 1st., 1st selection, teacher has 31 choices, to NOT select teesha, she has 30 other options, so, 30/31 2nd selection, teacher now have 30 other choices, and to select teesha, she have to pick her, so 1/30 so, overall for 1st case, it'll be 30/31*1/30 = 1/31 got this ?

18. hartnn

since the 2 cases are independent, you'll add them, 1/31 + 1/31 = 2/31

19. 10_CuspofPower_10

Ok then

20. 10_CuspofPower_10

So 2/31 * 1/31 would = 2/31 as the answer? Lol, or am I too early?

21. hartnn

1/31 + 1/31 = 2/31 thats why 2/31 is the answer as we considered both the cases.

22. 10_CuspofPower_10

Ohhhhhhh lol ok, I understand that now :b

23. 10_CuspofPower_10

Thank you [: You've been fanned lol.

24. hartnn

thanks for fanning! :D and welcome ^_^