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

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