Hi nitya34,
Let testers be T1, T2, T3,......T15,......T29, T30
Now since we have to find out the minimum no. of testers who passed the test, we can assume that
1.) Examiner C passed first 15 testers i.e., T1, T2, T3,......T14, T15
2.) Now since Examiner B passed 17 testers, there have to be at least 2 testers who were passed by both examiner C & B.
Let Examiner B passed T14, T15, T16, T17,......,T29, T30
3.)
Now here's the trap: Don't assume that since examiner B & C already got 2 testers in common, and as we know that examiner A passed 20 testers, we can conclude that at least 2 testers passed the test.
Though we can have the following scenario,
Total no. of testers passed by examiner A (20) ---> T11, T12, T13, T14, T15, T16, T17,......,T29, T30
Total no. of testers passed by examiner B (17) ---> T14, T15, T16, T17,......,T29, T30
Total no. of testers passed by examiner C (15) ---> T1, T2, T3,....T14, T15
where there are 2 common testers,
but we can also have the following scenario,
Total no. of testers passed by examiner A (20) ---> T1,T2,T3,.....,T8,T9,T10,T20,T21,T22,......,T28,T29,T30
Total no. of testers passed by examiner B (17) ---> T14, T15, T16, T17,......,T29, T30
Total no. of testers passed by examiner C (15) ---> T1, T2, T3,....T14, T15
where there are NO common testers.
So, my choice is
0 testers passed.
Hope that helps.
Regards,
Technext