q: A man rows his boat 90 km downstream and 5` km upstream, taking 3 hours each time. Find the speed of the stream?
Options:
(A) 7 kmph
(B) 5 kmph
(C) 2 kmph
(D) 8 kmph
(E) 1 kmph
a: Speed downstream = d/t = 90/(3) = 30 kmph
Speed upstream = d/t = 51/(3) = 17 kmph
The speed of the stream = (30 - 17)/2 = 7 kmph The answer is (A).
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q: In 2005, 30 percent of the math department’s 40 students were female, and in 2007, 40 percent of the math department’s 65 students were female. What was the percent increase from 2005 to 2007 in the number of female students in the department?
Options:
(A) 15%
(B) 116%
(C) 136%
(D) 155%
(E) 160%
a: Female students in 2005 = 30% of 40 = 12
Female students in 2007 = 40% of 65 = 26
Percentage increase = [(26 - 12)/12] *100 % = 116% The answer is (B).
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q: The average of 20 numbers is zero. Of them, at the most, how many may be greater than zero?
Options:
(A) 17
(B) 16
(C) 17
(D) 19
(E) 62
a: Average of 20 numbers = 0
Sum of 20 numbers = (0 * 20) = 0
It is quite possible that 19 of these numbers may be positive and if their sum is a, then 20th number is (-a). The answer is (D).
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q: In what time a sum of money double itself at 3% per annum simple interest?
Options:
(A) 33 1/8%
(B) 33 1/3%
(C) 33 3/3%
(D) 33 1/7%
(E) 32 1/3%
a:

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
P = (P*3*R)/100
R = 33 1/3% The answer is (B).
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