Rationale: 1/20 - 1/30 = 1/60
60 minutes
The answer: (C)
Question: A pipe can fill a cistern in 20 minutes whereas the cistern when fill can be emptied by a leak in 30 minutes. When both pipes are opened, find when the cistern will be full?
Options:
(A) 17 minutes
(B) 87 minutes
(C) 60 minutes
(D) 27 minutes
(E) 11 minutes
Reasoning: First even minus first odd = 2-1 = 1;
The sum of first 2 even integers minus the sum of first 2 odd integers = (2+4)-(1+3) = 2;
The sum of first 3 even integers minus the sum of first 3 odd integers = (2+4+6)-(1+3+5) = 3;
We can see the patterns here, so the sum of first 40 positive even integers minus the sum of first 40 positive odd integers will be 40.
Ans: (C)
Question: If X is the sum of first 40 positive even integers and Y is the sum of first 40 positive odd integers, what is the value of x-y?
Please try to explain your answers
Options:
(A) 0
(B) 25
(C) 40
(D) 75
(E) 100
Rationale: Since average price of a pencil = 2
Price of 75 pencils = 150
Price of 30 pens = (570 150) = 360
Average price of a pen = 42060 = 14
The answer: (E)
Question: 30 pens and 75 pencils were purchased for 570. If the average price of a pencil was 2.00, find the average price of a pen.
Options:
(A) 10
(B) 11
(C) 12
(D) 13
(E) 14
Reasoning: The number of children going to the picnic are 25
The answer will be D because only 75 is divisible by 25
Ans: (D)
Question: 25 children are going to a picnic. What is the smallest number of cakes that must be brought to the picnic so that each child receives the same number of cakes?
Options:
(A) 35
(B) 40
(C) 15
(D) 75
(E) 9
Rationale: For every natural number n, (y^n - b^n) is completely divisible by (y - b).
The answer: (C)
Question: (y^n - b^n) is completely divisible by (y - b), when
Options:
(A) n is odd natural number
(B) n is even natural number
(C) n is any natural number
(D) n is prime
(E) None
Rationale: Simple interest = (18000 * 4 * 15)/100 = Rs. 10800
Amount = P + I = 18000 + 10800 = Rs. 28800
The answer: (D)
Question: What amount does Kiran get if he invests Rs. 18000 at 15% p.a. simple interest for four years?
Options:
(A) 3888
(B) 26989
(C) 26700
(D) 28800
(E) 2879