Rationale: 1/20 - 1/28 = 1/70
70 minutes
The answer: (C)
Question: A pipe can fill a cistern in 20 minutes whereas the cistern when full can be emptied by a leak in 28 minutes. When both pipes are opened, find when the cistern will be full?
Options:
(A) 17
(B) 16
(C) 70
(D) 13
(E) 12
Reasoning: The total distance D traveled by John is given by
D = 45 * 2 + 3 * 50 = 240 miles.
Ans: (C)
Question: John left home and drove at the rate of 45 mph for 2 hours. He stopped for lunch then drove for another 3 hours at the rate of 50 mph to reach his destination. How many miles did John drive?
Options:
(A) 235 miles.
(B) 245 miles.
(C) 240 miles.
(D) 265 miles.
(E) 275 miles.
Rationale: 70 + 80 = 150 * 5/18 = 125/3 mps
D = 150 + 100 = 250 m
T = 250 * 3/125 = 6 se
The answer: (C)
Question: Two trains are moving at 80 kmph and 70 kmph in opposite directions. Their lengths are 150 m and 100 m respectively. The time they will take to pass each other completely is?
Options:
(A) 4 sec
(B) 5 sec
(C) 6 sec
(D) 7 sec
(E) 8 sec
Reasoning: 1: 2/5 = 5: 2
2/7 * 70 = 20
Ans: (B)
Question: A 70 cm long wire is to be cut into two pieces so that one piece will be 2/5th of the other, how many centimeters will the shorter piece be?
Options:
(A) 20
(B) 99
(C) 88
(D) 77
(E) 66
Rationale: Plug in an even integer; in this case 2
(3*2)-3 = 6-3 = 3 Odd
2+2^2 = 6 Even
(5*2)-3 = 10 - 3 = 7 Odd
(2*2)+1 = 4 + 1 = 5 Odd
(9*2)-5 = 18 - 5 = 13 Odd
The answer: (B)
Question: If x is an even integer, which of the following is an even integer?
Options:
(A) 3x-3
(B) x+x^2
(C) 5x-3
(D) 2x+1
(E) 9x-5
Rationale: Sum of 15 natural no. = 240/2 = 120
Average = 120/15 = 8
The answer: (B)

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
Question: The average of first 15 natural numbers is?
Options:
(A) 7
(B) 8
(C) 9
(D) 10
(E) 11