q: A and B can do a work in 18 days, B and C in 30 days and C and A in 36 days. In how many days will the work be completed, if all three of them work together?
Options:
(A) 360/13 days
(B) 350/13 days
(C) 160/13 days
(D) 260/13 days
(E) 960/13 days
a: Stream of consciousness: One day work of A and B = 1/18
One day work of B and C = 1/30
One day work of C and A = 1/36
2(A + B + C) = 1/18 + 1/30 + 1/36
2(A + B + C) = 21/180
(A + B + C) = 13/360
Number of days required = 360/13 days. The answer is (A).

question: At 15:00 there were 20 students in the computer lab. At 15:03 and every three minutes after that, 3 students entered the lab. If at 15:10 and every ten minutes after that 7 students left the lab, how many students were in the computer lab at 15:44 ?
Options:
(A) 7
(B) 14
(C) 25
(D) 27
(E) 30
answer: Stream of consciousness: Initial no of students + 3 * (1 + No of possible 3 minute intervals between 15:03 and 15:44) -
8 *(1 + No of possible 10 minute intervals between 15:10 and 15:44)
20 + 3*14 -8 * 4 = 25 The answer is (C).

q: The average age of a class of 14 students is 10 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) 32 Years
(D) 34 Years
(E) 25 Years
a: Stream of consciousness: Total age of students is 14X10 = 140 Years
Total age inclusive of teacher = 15X (10+1) = 165
So, Teacher's age is 165-140 = 25 Yrs
There is a shortcut for these type of problems
Teacher's age is 10+(15X1) = 25 Years The answer is (E).

question: The balance of a trader weighs 10% less than it should. Still the trader marks up his goods to get an overall profit of 20%. What is the mark up on the cost price?
Options:
(A) 40%
(B) 8%
(C) 25%
(D) 16.66%
(E) 9%
answer: Stream of consciousness: Original cost before weight adjustment: X
Cost after 90% weight adjustment: 9/10 X
20% profit on 9/10X: (120/100)(9/10)(X) or 108X/100
Mark up on original cost of X: (108X/100)/X-1 = 8/100 The answer is (B).

q: A train running at the speed of 60 km/hr crosses a pole in 12 seconds. Find the length of the train.
Options:
(A) 175 m
(B) 145 m
(C) 140 m
(D) 200 m
(E) 155 m
a: Stream of consciousness: Speed = 60*(5/18) m/sec = 50/3 m/sec
Length of Train (Distance) = Speed * Time
(50/3) * 12 = 200 meter The answer is (D).

q: 85 white and black tiles will be used to form a 10x10 square pattern. If there must be at least one black tile in every row and at least one white tile in every column, what is the maximum difference between the number of black and white tiles that can be used?
Options:
(A) 75
(B) 80
(C) 85
(D) 90
(E) 95
a:
Stream of consciousness: Answer = A
Please refer diagram below
85 - 10 = 75 The answer is (A).