question:Find the invalid no.from the following series 13, 18, 25, 30, 37, 40
Options:
(A) 21
(B) 25
(C) 40
(D) 47
(E) 58
answer:(C)
Stream of consciousness:The differences between two successive terms from the beginning are 7, 5, 7, 5, 7, 5. So, 40 is wrong.

question:Ravi can do a piece of work in 30 days while Prakash can do it in 40 days. In how many days will they finish it together?
Options:
(A) 19 1/7 days
(B) 16 1/7 days
(C) 14 1/7 days
(D) 17 1/7 days
(E) 13 1/7 days
answer:(D)
Stream of consciousness:1/30 + 1/40 = 7/120
120/7 = 17 1/7 days

question:The average age of a class of 39 students is 15 years. If the age of the teacher be included, then the average increases by 3 months .Find the age of the teacher.
Options:
(A) 22
(B) 25
(C) 8
(D) 27
(E) 19
answer:
(B)
Stream of consciousness:Sum of the ages of the students = 3915 = 585
New average = 15 years 3 months = 15 + 1414 year
Sum of the ages of students and teacher = 4015141514 = 40614614 = 610
Teacher age = 610 585 = 25 years.