q: The average of 13 numbers is 60. Average of the first 7 of them is 57 and that of the last 7 is 61. Find the 8th number?
Options:
(A) 46
(B) 77
(C) 88
(D) 544
(E) 33
a: Stream of consciousness: Sum of all the 13 numbers = 13 * 60 = 780
Sum of the first 7 of them = 7 * 57 = 399
Sum of the last 7 of them = 7 * 61 = 427
So, the 8th number = 427 + 399 - 780 = 46. The answer is (A).
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q: A train of 24 carriages, each of 60 meters length, when an engine also of 60 meters length is running at a speed of 60 kmph. In what time will the train cross a bridge 1.5 km long?
Options:
(A) 4
(B) 3
(C) 5
(D) 7
(E) 9
a: Stream of consciousness: D = 25 * 60 + 1500 = 3000 m
T = 3000/60 * 18/5 = 180 sec = 3 mins The answer is (B).
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q: The average age of a family of 6 members is 28 years.If the age of the youngest member is 7 years,what was the average age of the family at the birth of the youngest member?
Options:
(A) 15
(B) 18
(C) 21
(D) 12
(E) 19
a:
Stream of consciousness: Present age of total members = 6 X 28 = 168
7 yrs back their ages were = 6 x 7 = 42
Ages at the birth of youngest member = 168 - 42 = 126
Therefore, avg age at the birth of youngest member = 126/6 = 21. The answer is (C).
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