Question : The probability that a teacher will give an unannounced test during any class meeting is 1/5. If a student is absent twice, then the probability that the student will miss at least one test is
(A) 4/5
(B) 2/5
(C) 7/25
(D) 9/25
Answer : option (D)
Solution :
The probability that one test is held is 2 × (1 × 5) × (4× 5)= 8/25. The probability that test is held on both days is (1 × 5) × (1 × 5)= 1/25. Therefore, the probability that the student misses at least one test is 8/25+1/25=9/25