q: The average age of a class of 12 students is 8 yrs. if the teacher's age is also included, the average increases by one year. Find the age of the teacher
Options:
(A) 30 Years
(B) 31 Years
(C) 21 Years
(D) 34 Years
(E) 49 Years
a: Stream of consciousness: Total age of students is 12X8 = 96 Years
Total age inclusive of teacher = 13X (8+1) = 117
So, Teacher's age is 117-96 = 21 Yrs
There is a shortcut for these type of problems
Teacher's age is 8+(13X1) = 21 Years The answer is (C).
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q: he population of a city is 150,000. If it increases at the rate of 6% per annum, then what will be its population 2 years hence?
Options:
(A) 1697787
(B) 1697723
(C) 168540
(D) 169728
(E) 169718
a: Stream of consciousness: Population after n years = P [1 + (R/100)]2
Population after 2 years = 150000 * [1 + 6/100]2 = (150000 x 53/50 x 53/50) = 168540 The answer is (C).
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q: The least number of complete years in which a sum of money put out at 20% C.I. will be more than doubled is?
Options:
(A) 3
(B) 4
(C) 5
(D) 6
(E) 7
a:
Stream of consciousness: P(1 + 20/100)n > 2P or (6/5)n > 2
Now, (6/5 * 6/5 * 6/5 * 6/5) > 2. So, n = 4 years. The answer is (B).
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